Subject: [PATCH v5 07/14] KVM: ARM: World-switch implementation

From: [email-masked] (Gleb Natapov)
Date: Wed, 16 Jan 2013 14:12:38 +0200

On Tue, Jan 15, 2013 at 09:08:11PM -0500, Christoffer Dall wrote:
> On Tue, Jan 15, 2013 at 4:43 AM, Gleb Natapov <[email-masked]> wrote:
> > On Tue, Jan 08, 2013 at 01:39:24PM -0500, Christoffer Dall wrote:
> >> Provides complete world-switch implementation to switch to other guests
> >> running in non-secure modes. Includes Hyp exception handlers that
> >> capture necessary exception information and stores the information on
> >> the VCPU and KVM structures.
> >>
> >> The following Hyp-ABI is also documented in the code:
> >>
> >> Hyp-ABI: Calling HYP-mode functions from host (in SVC mode):
> >>    Switching to Hyp mode is done through a simple HVC #0 instruction. The
> >>    exception vector code will check that the HVC comes from VMID==0 and if
> >>    so will push the necessary state (SPSR, lr_usr) on the Hyp stack.
> >>    - r0 contains a pointer to a HYP function
> >>    - r1, r2, and r3 contain arguments to the above function.
> >>    - The HYP function will be called with its arguments in r0, r1 and r2.
> >>    On HYP function return, we return directly to SVC.
> >>
> >> A call to a function executing in Hyp mode is performed like the following:
> >>
> >>         <svc code>
> >>         ldr     r0, =BSYM(my_hyp_fn)
> >>         ldr     r1, =my_param
> >>         hvc #0  ; Call my_hyp_fn(my_param) from HYP mode
> >>         <svc code>
> >>
> >> Otherwise, the world-switch is pretty straight-forward. All state that
> >> can be modified by the guest is first backed up on the Hyp stack and the
> >> VCPU values is loaded onto the hardware. State, which is not loaded, but
> >> theoretically modifiable by the guest is protected through the
> >> virtualiation features to generate a trap and cause software emulation.
> >> Upon guest returns, all state is restored from hardware onto the VCPU
> >> struct and the original state is restored from the Hyp-stack onto the
> >> hardware.
> >>
> >> SMP support using the VMPIDR calculated on the basis of the host MPIDR
> >> and overriding the low bits with KVM vcpu_id contributed by Marc Zyngier.
> >>
> >> Reuse of VMIDs has been implemented by Antonios Motakis and adapated from
> >> a separate patch into the appropriate patches introducing the
> >> functionality. Note that the VMIDs are stored per VM as required by the ARM
> >> architecture reference manual.
> >>
> >> To support VFP/NEON we trap those instructions using the HPCTR. When
> >> we trap, we switch the FPU.  After a guest exit, the VFP state is
> >> returned to the host.  When disabling access to floating point
> >> instructions, we also mask FPEXC_EN in order to avoid the guest
> >> receiving Undefined instruction exceptions before we have a chance to
> >> switch back the floating point state.  We are reusing vfp_hard_struct,
> >> so we depend on VFPv3 being enabled in the host kernel, if not, we still
> >> trap cp10 and cp11 in order to inject an undefined instruction exception
> >> whenever the guest tries to use VFP/NEON. VFP/NEON developed by
> >> Antionios Motakis and Rusty Russell.
> >>
> >> Aborts that are permission faults, and not stage-1 page table walk, do
> >> not report the faulting address in the HPFAR.  We have to resolve the
> >> IPA, and store it just like the HPFAR register on the VCPU struct. If
> >> the IPA cannot be resolved, it means another CPU is playing with the
> >> page tables, and we simply restart the guest.  This quirk was fixed by
> >> Marc Zyngier.
> >>
> >> Reviewed-by: Marcelo Tosatti <[email-masked]>
> >> Signed-off-by: Rusty Russell <[email-masked]>
> >> Signed-off-by: Antonios Motakis <[email-masked]>
> >> Signed-off-by: Marc Zyngier <[email-masked]>
> >> Signed-off-by: Christoffer Dall <[email-masked]>
> >> ---
> >>  arch/arm/include/asm/kvm_arm.h  |   51 ++++
> >>  arch/arm/include/asm/kvm_host.h |   10 +
> >>  arch/arm/kernel/asm-offsets.c   |   25 ++
> >>  arch/arm/kvm/arm.c              |  187 ++++++++++++++++
> >>  arch/arm/kvm/interrupts.S       |  396 +++++++++++++++++++++++++++++++++++
> >>  arch/arm/kvm/interrupts_head.S  |  443 +++++++++++++++++++++++++++++++++++++++
> >>  6 files changed, 1108 insertions(+), 4 deletions(-)
> >>  create mode 100644 arch/arm/kvm/interrupts_head.S
> >>
> >> diff --git a/arch/arm/include/asm/kvm_arm.h b/arch/arm/include/asm/kvm_arm.h
> >> index fb22ee8..a3262a2 100644
> >> --- a/arch/arm/include/asm/kvm_arm.h
> >> +++ b/arch/arm/include/asm/kvm_arm.h
> >> @@ -98,6 +98,18 @@
> >>  #define TTBCR_T0SZ   3
> >>  #define HTCR_MASK    (TTBCR_T0SZ | TTBCR_IRGN0 | TTBCR_ORGN0 | TTBCR_SH0)
> >>
> >> +/* Hyp System Trap Register */
> >> +#define HSTR_T(x)    (1 << x)
> >> +#define HSTR_TTEE    (1 << 16)
> >> +#define HSTR_TJDBX   (1 << 17)
> >> +
> >> +/* Hyp Coprocessor Trap Register */
> >> +#define HCPTR_TCP(x) (1 << x)
> >> +#define HCPTR_TCP_MASK       (0x3fff)
> >> +#define HCPTR_TASE   (1 << 15)
> >> +#define HCPTR_TTA    (1 << 20)
> >> +#define HCPTR_TCPAC  (1 << 31)
> >> +
> >>  /* Hyp Debug Configuration Register bits */
> >>  #define HDCR_TDRA    (1 << 11)
> >>  #define HDCR_TDOSA   (1 << 10)
> >> @@ -144,6 +156,45 @@
> >>  #else
> >>  #define VTTBR_X              (5 - KVM_T0SZ)
> >>  #endif
> >> +#define VTTBR_BADDR_SHIFT (VTTBR_X - 1)
> >> +#define VTTBR_BADDR_MASK  (((1LLU << (40 - VTTBR_X)) - 1) << VTTBR_BADDR_SHIFT)
> >> +#define VTTBR_VMID_SHIFT  (48LLU)
> >> +#define VTTBR_VMID_MASK        (0xffLLU << VTTBR_VMID_SHIFT)
> >> +
> >> +/* Hyp Syndrome Register (HSR) bits */
> >> +#define HSR_EC_SHIFT (26)
> >> +#define HSR_EC               (0x3fU << HSR_EC_SHIFT)
> >> +#define HSR_IL               (1U << 25)
> >> +#define HSR_ISS              (HSR_IL - 1)
> >> +#define HSR_ISV_SHIFT        (24)
> >> +#define HSR_ISV              (1U << HSR_ISV_SHIFT)
> >> +#define HSR_FSC              (0x3f)
> >> +#define HSR_FSC_TYPE (0x3c)
> >> +#define HSR_WNR              (1 << 6)
> >> +
> >> +#define FSC_FAULT    (0x04)
> >> +#define FSC_PERM     (0x0c)
> >> +
> >> +/* Hyp Prefetch Fault Address Register (HPFAR/HDFAR) */
> >> +#define HPFAR_MASK   (~0xf)
> >>
> >> +#define HSR_EC_UNKNOWN       (0x00)
> >> +#define HSR_EC_WFI   (0x01)
> >> +#define HSR_EC_CP15_32       (0x03)
> >> +#define HSR_EC_CP15_64       (0x04)
> >> +#define HSR_EC_CP14_MR       (0x05)
> >> +#define HSR_EC_CP14_LS       (0x06)
> >> +#define HSR_EC_CP_0_13       (0x07)
> >> +#define HSR_EC_CP10_ID       (0x08)
> >> +#define HSR_EC_JAZELLE       (0x09)
> >> +#define HSR_EC_BXJ   (0x0A)
> >> +#define HSR_EC_CP14_64       (0x0C)
> >> +#define HSR_EC_SVC_HYP       (0x11)
> >> +#define HSR_EC_HVC   (0x12)
> >> +#define HSR_EC_SMC   (0x13)
> >> +#define HSR_EC_IABT  (0x20)
> >> +#define HSR_EC_IABT_HYP      (0x21)
> >> +#define HSR_EC_DABT  (0x24)
> >> +#define HSR_EC_DABT_HYP      (0x25)
> >>
> >>  #endif /* __ARM_KVM_ARM_H__ */
> >> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> >> index 1de6f0d..ddb09da 100644
> >> --- a/arch/arm/include/asm/kvm_host.h
> >> +++ b/arch/arm/include/asm/kvm_host.h
> >> @@ -21,6 +21,7 @@
> >>
> >>  #include <asm/kvm.h>
> >>  #include <asm/kvm_asm.h>
> >> +#include <asm/fpstate.h>
> >>
> >>  #define KVM_MAX_VCPUS CONFIG_KVM_ARM_MAX_VCPUS
> >>  #define KVM_USER_MEM_SLOTS 32
> >> @@ -85,6 +86,14 @@ struct kvm_vcpu_arch {
> >>       u32 hxfar;              /* Hyp Data/Inst Fault Address Register */
> >>       u32 hpfar;              /* Hyp IPA Fault Address Register */
> >>
> >> +     /* Floating point registers (VFP and Advanced SIMD/NEON) */
> >> +     struct vfp_hard_struct vfp_guest;
> >> +     struct vfp_hard_struct *vfp_host;
> >> +
> >> +     /*
> >> +      * Anything that is not used directly from assembly code goes
> >> +      * here.
> >> +      */
> >>       /* Interrupt related fields */
> >>       u32 irq_lines;          /* IRQ and FIQ levels */
> >>
> >> @@ -112,6 +121,7 @@ struct kvm_one_reg;
> >>  int kvm_arm_get_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg);
> >>  int kvm_arm_set_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg);
> >>  u64 kvm_call_hyp(void *hypfn, ...);
> >> +void force_vm_exit(const cpumask_t *mask);
> >>
> >>  #define KVM_ARCH_WANT_MMU_NOTIFIER
> >>  struct kvm;
> >> diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c
> >> index c985b48..c8b3272 100644
> >> --- a/arch/arm/kernel/asm-offsets.c
> >> +++ b/arch/arm/kernel/asm-offsets.c
> >> @@ -13,6 +13,9 @@
> >>  #include <linux/sched.h>
> >>  #include <linux/mm.h>
> >>  #include <linux/dma-mapping.h>
> >> +#ifdef CONFIG_KVM_ARM_HOST
> >> +#include <linux/kvm_host.h>
> >> +#endif
> >>  #include <asm/cacheflush.h>
> >>  #include <asm/glue-df.h>
> >>  #include <asm/glue-pf.h>
> >> @@ -146,5 +149,27 @@ int main(void)
> >>    DEFINE(DMA_BIDIRECTIONAL,  DMA_BIDIRECTIONAL);
> >>    DEFINE(DMA_TO_DEVICE,              DMA_TO_DEVICE);
> >>    DEFINE(DMA_FROM_DEVICE,    DMA_FROM_DEVICE);
> >> +#ifdef CONFIG_KVM_ARM_HOST
> >> +  DEFINE(VCPU_KVM,           offsetof(struct kvm_vcpu, kvm));
> >> +  DEFINE(VCPU_MIDR,          offsetof(struct kvm_vcpu, arch.midr));
> >> +  DEFINE(VCPU_CP15,          offsetof(struct kvm_vcpu, arch.cp15));
> >> +  DEFINE(VCPU_VFP_GUEST,     offsetof(struct kvm_vcpu, arch.vfp_guest));
> >> +  DEFINE(VCPU_VFP_HOST,              offsetof(struct kvm_vcpu, arch.vfp_host));
> >> +  DEFINE(VCPU_REGS,          offsetof(struct kvm_vcpu, arch.regs));
> >> +  DEFINE(VCPU_USR_REGS,              offsetof(struct kvm_vcpu, arch.regs.usr_regs));
> >> +  DEFINE(VCPU_SVC_REGS,              offsetof(struct kvm_vcpu, arch.regs.svc_regs));
> >> +  DEFINE(VCPU_ABT_REGS,              offsetof(struct kvm_vcpu, arch.regs.abt_regs));
> >> +  DEFINE(VCPU_UND_REGS,              offsetof(struct kvm_vcpu, arch.regs.und_regs));
> >> +  DEFINE(VCPU_IRQ_REGS,              offsetof(struct kvm_vcpu, arch.regs.irq_regs));
> >> +  DEFINE(VCPU_FIQ_REGS,              offsetof(struct kvm_vcpu, arch.regs.fiq_regs));
> >> +  DEFINE(VCPU_PC,            offsetof(struct kvm_vcpu, arch.regs.usr_regs.ARM_pc));
> >> +  DEFINE(VCPU_CPSR,          offsetof(struct kvm_vcpu, arch.regs.usr_regs.ARM_cpsr));
> >> +  DEFINE(VCPU_IRQ_LINES,     offsetof(struct kvm_vcpu, arch.irq_lines));
> >> +  DEFINE(VCPU_HSR,           offsetof(struct kvm_vcpu, arch.hsr));
> >> +  DEFINE(VCPU_HxFAR,         offsetof(struct kvm_vcpu, arch.hxfar));
> >> +  DEFINE(VCPU_HPFAR,         offsetof(struct kvm_vcpu, arch.hpfar));
> >> +  DEFINE(VCPU_HYP_PC,                offsetof(struct kvm_vcpu, arch.hyp_pc));
> >> +  DEFINE(KVM_VTTBR,          offsetof(struct kvm, arch.vttbr));
> >> +#endif
> >>    return 0;
> >>  }
> >> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> >> index 9b4566e..c94d278 100644
> >> --- a/arch/arm/kvm/arm.c
> >> +++ b/arch/arm/kvm/arm.c
> >> @@ -40,6 +40,7 @@
> >>  #include <asm/kvm_arm.h>
> >>  #include <asm/kvm_asm.h>
> >>  #include <asm/kvm_mmu.h>
> >> +#include <asm/kvm_emulate.h>
> >>
> >>  #ifdef REQUIRES_VIRT
> >>  __asm__(".arch_extension     virt");
> >> @@ -49,6 +50,10 @@ static DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
> >>  static struct vfp_hard_struct __percpu *kvm_host_vfp_state;
> >>  static unsigned long hyp_default_vectors;
> >>
> >> +/* The VMID used in the VTTBR */
> >> +static atomic64_t kvm_vmid_gen = ATOMIC64_INIT(1);
> >> +static u8 kvm_next_vmid;
> >> +static DEFINE_SPINLOCK(kvm_vmid_lock);
> >>
> >>  int kvm_arch_hardware_enable(void *garbage)
> >>  {
> >> @@ -276,6 +281,8 @@ int __attribute_const__ kvm_target_cpu(void)
> >>
> >>  int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
> >>  {
> >> +     /* Force users to call KVM_ARM_VCPU_INIT */
> >> +     vcpu->arch.target = -1;
> >>       return 0;
> >>  }
> >>
> >> @@ -286,6 +293,7 @@ void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu)
> >>  void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
> >>  {
> >>       vcpu->cpu = cpu;
> >> +     vcpu->arch.vfp_host = this_cpu_ptr(kvm_host_vfp_state);
> >>  }
> >>
> >>  void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
> >> @@ -318,12 +326,189 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
> >>
> >>  int kvm_arch_vcpu_in_guest_mode(struct kvm_vcpu *v)
> > As far as I see the function is unused.
> >
> >>  {
> >> +     return v->mode == IN_GUEST_MODE;
> >> +}
> >> +
> >> +/* Just ensure a guest exit from a particular CPU */
> >> +static void exit_vm_noop(void *info)
> >> +{
> >> +}
> >> +
> >> +void force_vm_exit(const cpumask_t *mask)
> >> +{
> >> +     smp_call_function_many(mask, exit_vm_noop, NULL, true);
> >> +}
> > There is make_all_cpus_request() for that. It actually sends IPIs only
> > to cpus that are running vcpus.
> >
> >> +
> >> +/**
> >> + * need_new_vmid_gen - check that the VMID is still valid
> >> + * @kvm: The VM's VMID to checkt
> >> + *
> >> + * return true if there is a new generation of VMIDs being used
> >> + *
> >> + * The hardware supports only 256 values with the value zero reserved for the
> >> + * host, so we check if an assigned value belongs to a previous generation,
> >> + * which which requires us to assign a new value. If we're the first to use a
> >> + * VMID for the new generation, we must flush necessary caches and TLBs on all
> >> + * CPUs.
> >> + */
> >> +static bool need_new_vmid_gen(struct kvm *kvm)
> >> +{
> >> +     return unlikely(kvm->arch.vmid_gen != atomic64_read(&kvm_vmid_gen));
> >> +}
> >> +
> >> +/**
> >> + * update_vttbr - Update the VTTBR with a valid VMID before the guest runs
> >> + * @kvm      The guest that we are about to run
> >> + *
> >> + * Called from kvm_arch_vcpu_ioctl_run before entering the guest to ensure the
> >> + * VM has a valid VMID, otherwise assigns a new one and flushes corresponding
> >> + * caches and TLBs.
> >> + */
> >> +static void update_vttbr(struct kvm *kvm)
> >> +{
> >> +     phys_addr_t pgd_phys;
> >> +     u64 vmid;
> >> +
> >> +     if (!need_new_vmid_gen(kvm))
> >> +             return;
> >> +
> >> +     spin_lock(&kvm_vmid_lock);
> >> +
> >> +     /*
> >> +      * We need to re-check the vmid_gen here to ensure that if another vcpu
> >> +      * already allocated a valid vmid for this vm, then this vcpu should
> >> +      * use the same vmid.
> >> +      */
> >> +     if (!need_new_vmid_gen(kvm)) {
> >> +             spin_unlock(&kvm_vmid_lock);
> >> +             return;
> >> +     }
> >> +
> >> +     /* First user of a new VMID generation? */
> >> +     if (unlikely(kvm_next_vmid == 0)) {
> >> +             atomic64_inc(&kvm_vmid_gen);
> >> +             kvm_next_vmid = 1;
> >> +
> >> +             /*
> >> +              * On SMP we know no other CPUs can use this CPU's or each
> >> +              * other's VMID after force_vm_exit returns since the
> >> +              * kvm_vmid_lock blocks them from reentry to the guest.
> >> +              */
> >> +             force_vm_exit(cpu_all_mask);
> >> +             /*
> >> +              * Now broadcast TLB + ICACHE invalidation over the inner
> >> +              * shareable domain to make sure all data structures are
> >> +              * clean.
> >> +              */
> >> +             kvm_call_hyp(__kvm_flush_vm_context);
> >> +     }
> >> +
> >> +     kvm->arch.vmid_gen = atomic64_read(&kvm_vmid_gen);
> >> +     kvm->arch.vmid = kvm_next_vmid;
> >> +     kvm_next_vmid++;
> >> +
> >> +     /* update vttbr to be used with the new vmid */
> >> +     pgd_phys = virt_to_phys(kvm->arch.pgd);
> >> +     vmid = ((u64)(kvm->arch.vmid) << VTTBR_VMID_SHIFT) & VTTBR_VMID_MASK;
> >> +     kvm->arch.vttbr = pgd_phys & VTTBR_BADDR_MASK;
> >> +     kvm->arch.vttbr |= vmid;
> >> +
> >> +     spin_unlock(&kvm_vmid_lock);
> >> +}
> >> +
> >> +/*
> >> + * Return > 0 to return to guest, < 0 on error, 0 (and set exit_reason) on
> >> + * proper exit to QEMU.
> >> + */
> >> +static int handle_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
> >> +                    int exception_index)
> >> +{
> >> +     run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
> >>       return 0;
> >>  }
> >>
> >> +/**
> >> + * kvm_arch_vcpu_ioctl_run - the main VCPU run function to execute guest code
> >> + * @vcpu:    The VCPU pointer
> >> + * @run:     The kvm_run structure pointer used for userspace state exchange
> >> + *
> >> + * This function is called through the VCPU_RUN ioctl called from user space. It
> >> + * will execute VM code in a loop until the time slice for the process is used
> >> + * or some emulation is needed from user space in which case the function will
> >> + * return with return value 0 and with the kvm_run structure filled in with the
> >> + * required data for the requested emulation.
> >> + */
> >>  int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
> >>  {
> >> -     return -EINVAL;
> >> +     int ret;
> >> +     sigset_t sigsaved;
> >> +
> >> +     /* Make sure they initialize the vcpu with KVM_ARM_VCPU_INIT */
> >> +     if (unlikely(vcpu->arch.target < 0))
> >> +             return -ENOEXEC;
> >> +
> >> +     if (vcpu->sigset_active)
> >> +             sigprocmask(SIG_SETMASK, &vcpu->sigset, &sigsaved);
> >> +
> >> +     ret = 1;
> >> +     run->exit_reason = KVM_EXIT_UNKNOWN;
> >> +     while (ret > 0) {
> >> +             /*
> >> +              * Check conditions before entering the guest
> >> +              */
> >> +             cond_resched();
> >> +
> >> +             update_vttbr(vcpu->kvm);
> >> +
> >> +             local_irq_disable();
> >> +
> >> +             /*
> >> +              * Re-check atomic conditions
> >> +              */
> >> +             if (signal_pending(current)) {
> >> +                     ret = -EINTR;
> >> +                     run->exit_reason = KVM_EXIT_INTR;
> >> +             }
> >> +
> >> +             if (ret <= 0 || need_new_vmid_gen(vcpu->kvm)) {
> >> +                     local_irq_enable();
> >> +                     continue;
> >> +             }
> >> +
> >> +             /**************************************************************
> >> +              * Enter the guest
> >> +              */
> >> +             trace_kvm_entry(*vcpu_pc(vcpu));
> >> +             kvm_guest_enter();
> >> +             vcpu->mode = IN_GUEST_MODE;
> > You need to set mode to IN_GUEST_MODE before disabling interrupt and
> > check that mode != EXITING_GUEST_MODE after disabling interrupt but
> > before entering the guest. This way you will catch kicks that were sent
> > between setting of the mode and disabling the interrupts. Also you need
> > to check vcpu->requests and exit if it is not empty. I see that you do
> > not use vcpu->requests at all, but you should since common kvm code
> > assumes that it is used. make_all_cpus_request() uses it for instance.
> >
> 
> I don't quite agree, but almost:
> 
> Why would you set IN_GUEST_MODE before disabling interrupts? The only
> reason I can see for to be a requirement is to leverage an implicit
> memory barrier. Receiving the IPI in this little window does nothing
> (the smp_cross_call is a noop).
> 
> Checking that mode != EXITING_GUEST_MODE is equally useless in my
> opinion, as I read the requests code the only reason for this mode is
> to avoid sending an IPI twice.
> 
> Kicks sent between setting the mode and disabling the interrupts is
> not the point, the point is to check the requests field (which we
> don't use at all on ARM, and generic code also doesn't use on ARM)
> after disabling interrupts, and after setting IN_GUEST_MODE.
> 
Yes, you are right. There is not race here.

> The patch below fixes your issues, and while I would push back on
> anything else than direct bug fixes at this point, the current code is
> semantically incorrect wrt. KVM vcpu requests, so it's worth a fix,
> and the patch itself is trivial.
> 
> >> +
> >> +             ret = kvm_call_hyp(__kvm_vcpu_run, vcpu);
> > You do not take kvm->srcu lock before entering the guest. It looks
> > wrong.
> >
> 
> why would I take that before entering the guest? The only thing the
Right. No need to take it before entering a guest of course. I should
have said "after". Anyway absents of srcu handling raced my suspicion
and made me check all the code for kvm->srcu handling. I expected to see
kvm->srcu handling in vcpu_run() because x86 locks srcu at the beginning
of vcpu loop, release it before guest entry and retakes it after exit.
This way all the code called from vcpu run loop is protected. This is of
course not the only way to tackle it and you can do locking only around
memslot use.

> read side RCU protects against is the memslots data structure as far
> as I can see, so the second patch pasted below fixes this for the code
> that actually accesses this data structure.
Many memory related functions that you call access memslots under the
hood and assume that locking is done by the caller. From the quick look
I found those that you've missed:
kvm_is_visible_gfn()
kvm_read_guest()
gfn_to_hva()
gfn_to_pfn_prot()
kvm_memslots()

May be there are more. Can you enable RCU debugging in your kernel config
and check? This does not guaranty that it will catch all of the places,
but better than nothing.

> 
> >> +
> >> +             vcpu->mode = OUTSIDE_GUEST_MODE;
> >> +             kvm_guest_exit();
> >> +             trace_kvm_exit(*vcpu_pc(vcpu));
> >> +             /*
> >> +              * We may have taken a host interrupt in HYP mode (ie
> >> +              * while executing the guest). This interrupt is still
> >> +              * pending, as we haven't serviced it yet!
> >> +              *
> >> +              * We're now back in SVC mode, with interrupts
> >> +              * disabled.  Enabling the interrupts now will have
> >> +              * the effect of taking the interrupt again, in SVC
> >> +              * mode this time.
> >> +              */
> >> +             local_irq_enable();
> >> +
> >> +             /*
> >> +              * Back from guest
> >> +              *************************************************************/
> >> +
> >> +             ret = handle_exit(vcpu, run, ret);
> >> +     }
> >> +
> >> +     if (vcpu->sigset_active)
> >> +             sigprocmask(SIG_SETMASK, &sigsaved, NULL);
> >> +     return ret;
> >>  }
> >>
> >>  static int vcpu_interrupt_line(struct kvm_vcpu *vcpu, int number, bool level)
> >> diff --git a/arch/arm/kvm/interrupts.S b/arch/arm/kvm/interrupts.S
> >> index a923590..08adcd5 100644
> >> --- a/arch/arm/kvm/interrupts.S
> >> +++ b/arch/arm/kvm/interrupts.S
> >> @@ -20,9 +20,12 @@
> >>  #include <linux/const.h>
> >>  #include <asm/unified.h>
> >>  #include <asm/page.h>
> >> +#include <asm/ptrace.h>
> >>  #include <asm/asm-offsets.h>
> >>  #include <asm/kvm_asm.h>
> >>  #include <asm/kvm_arm.h>
> >> +#include <asm/vfpmacros.h>
> >> +#include "interrupts_head.S"
> >>
> >>       .text
> >>
> >> @@ -31,36 +34,423 @@ __kvm_hyp_code_start:
> >>
> >>  /********************************************************************
> >>   * Flush per-VMID TLBs
> >> + *
> >> + * void __kvm_tlb_flush_vmid(struct kvm *kvm);
> >> + *
> >> + * We rely on the hardware to broadcast the TLB invalidation to all CPUs
> >> + * inside the inner-shareable domain (which is the case for all v7
> >> + * implementations).  If we come across a non-IS SMP implementation, we'll
> >> + * have to use an IPI based mechanism. Until then, we stick to the simple
> >> + * hardware assisted version.
> >>   */
> >>  ENTRY(__kvm_tlb_flush_vmid)
> >> +     push    {r2, r3}
> >> +
> >> +     add     r0, r0, #KVM_VTTBR
> >> +     ldrd    r2, r3, [r0]
> >> +     mcrr    p15, 6, r2, r3, c2      @ Write VTTBR
> >> +     isb
> >> +     mcr     p15, 0, r0, c8, c3, 0   @ TLBIALLIS (rt ignored)
> >> +     dsb
> >> +     isb
> >> +     mov     r2, #0
> >> +     mov     r3, #0
> >> +     mcrr    p15, 6, r2, r3, c2      @ Back to VMID #0
> >> +     isb                             @ Not necessary if followed by eret
> >> +
> >> +     pop     {r2, r3}
> >>       bx      lr
> >>  ENDPROC(__kvm_tlb_flush_vmid)
> >>
> >>  /********************************************************************
> >> - * Flush TLBs and instruction caches of current CPU for all VMIDs
> >> + * Flush TLBs and instruction caches of all CPUs inside the inner-shareable
> >> + * domain, for all VMIDs
> >> + *
> >> + * void __kvm_flush_vm_context(void);
> >>   */
> >>  ENTRY(__kvm_flush_vm_context)
> >> +     mov     r0, #0                  @ rn parameter for c15 flushes is SBZ
> >> +
> >> +     /* Invalidate NS Non-Hyp TLB Inner Shareable (TLBIALLNSNHIS) */
> >> +     mcr     p15, 4, r0, c8, c3, 4
> >> +     /* Invalidate instruction caches Inner Shareable (ICIALLUIS) */
> >> +     mcr     p15, 0, r0, c7, c1, 0
> >> +     dsb
> >> +     isb                             @ Not necessary if followed by eret
> >> +
> >>       bx      lr
> >>  ENDPROC(__kvm_flush_vm_context)
> >>
> >> +
> >>  /********************************************************************
> >>   *  Hypervisor world-switch code
> >> + *
> >> + *
> >> + * int __kvm_vcpu_run(struct kvm_vcpu *vcpu)
> >>   */
> >>  ENTRY(__kvm_vcpu_run)
> >> -     bx      lr
> >> +     @ Save the vcpu pointer
> >> +     mcr     p15, 4, vcpu, c13, c0, 2        @ HTPIDR
> >> +
> >> +     save_host_regs
> >> +
> >> +     @ Store hardware CP15 state and load guest state
> >> +     read_cp15_state store_to_vcpu = 0
> >> +     write_cp15_state read_from_vcpu = 1
> >> +
> >> +     @ If the host kernel has not been configured with VFPv3 support,
> >> +     @ then it is safer if we deny guests from using it as well.
> >> +#ifdef CONFIG_VFPv3
> >> +     @ Set FPEXC_EN so the guest doesn't trap floating point instructions
> >> +     VFPFMRX r2, FPEXC               @ VMRS
> >> +     push    {r2}
> >> +     orr     r2, r2, #FPEXC_EN
> >> +     VFPFMXR FPEXC, r2               @ VMSR
> >> +#endif
> >> +
> >> +     @ Configure Hyp-role
> >> +     configure_hyp_role vmentry
> >> +
> >> +     @ Trap coprocessor CRx accesses
> >> +     set_hstr vmentry
> >> +     set_hcptr vmentry, (HCPTR_TTA | HCPTR_TCP(10) | HCPTR_TCP(11))
> >> +     set_hdcr vmentry
> >> +
> >> +     @ Write configured ID register into MIDR alias
> >> +     ldr     r1, [vcpu, #VCPU_MIDR]
> >> +     mcr     p15, 4, r1, c0, c0, 0
> >> +
> >> +     @ Write guest view of MPIDR into VMPIDR
> >> +     ldr     r1, [vcpu, #CP15_OFFSET(c0_MPIDR)]
> >> +     mcr     p15, 4, r1, c0, c0, 5
> >> +
> >> +     @ Set up guest memory translation
> >> +     ldr     r1, [vcpu, #VCPU_KVM]
> >> +     add     r1, r1, #KVM_VTTBR
> >> +     ldrd    r2, r3, [r1]
> >> +     mcrr    p15, 6, r2, r3, c2      @ Write VTTBR
> >> +
> >> +     @ We're all done, just restore the GPRs and go to the guest
> >> +     restore_guest_regs
> >> +     clrex                           @ Clear exclusive monitor
> >> +     eret
> >> +
> >> +__kvm_vcpu_return:
> >> +     /*
> >> +      * return convention:
> >> +      * guest r0, r1, r2 saved on the stack
> >> +      * r0: vcpu pointer
> >> +      * r1: exception code
> >> +      */
> >> +     save_guest_regs
> >> +
> >> +     @ Set VMID == 0
> >> +     mov     r2, #0
> >> +     mov     r3, #0
> >> +     mcrr    p15, 6, r2, r3, c2      @ Write VTTBR
> >> +
> >> +     @ Don't trap coprocessor accesses for host kernel
> >> +     set_hstr vmexit
> >> +     set_hdcr vmexit
> >> +     set_hcptr vmexit, (HCPTR_TTA | HCPTR_TCP(10) | HCPTR_TCP(11))
> >> +
> >> +#ifdef CONFIG_VFPv3
> >> +     @ Save floating point registers we if let guest use them.
> >> +     tst     r2, #(HCPTR_TCP(10) | HCPTR_TCP(11))
> >> +     bne     after_vfp_restore
> >> +
> >> +     @ Switch VFP/NEON hardware state to the host's
> >> +     add     r7, vcpu, #VCPU_VFP_GUEST
> >> +     store_vfp_state r7
> >> +     add     r7, vcpu, #VCPU_VFP_HOST
> >> +     ldr     r7, [r7]
> >> +     restore_vfp_state r7
> >> +
> >> +after_vfp_restore:
> >> +     @ Restore FPEXC_EN which we clobbered on entry
> >> +     pop     {r2}
> >> +     VFPFMXR FPEXC, r2
> >> +#endif
> >> +
> >> +     @ Reset Hyp-role
> >> +     configure_hyp_role vmexit
> >> +
> >> +     @ Let host read hardware MIDR
> >> +     mrc     p15, 0, r2, c0, c0, 0
> >> +     mcr     p15, 4, r2, c0, c0, 0
> >> +
> >> +     @ Back to hardware MPIDR
> >> +     mrc     p15, 0, r2, c0, c0, 5
> >> +     mcr     p15, 4, r2, c0, c0, 5
> >> +
> >> +     @ Store guest CP15 state and restore host state
> >> +     read_cp15_state store_to_vcpu = 1
> >> +     write_cp15_state read_from_vcpu = 0
> >> +
> >> +     restore_host_regs
> >> +     clrex                           @ Clear exclusive monitor
> >> +     mov     r0, r1                  @ Return the return code
> >> +     bx      lr                      @ return to IOCTL
> >>
> >>  ENTRY(kvm_call_hyp)
> >> +     hvc     #0
> >>       bx      lr
> >>
> >>
> >>  /********************************************************************
> >>   * Hypervisor exception vector and handlers
> >> + *
> >> + *
> >> + * The KVM/ARM Hypervisor ABI is defined as follows:
> >> + *
> >> + * Entry to Hyp mode from the host kernel will happen _only_ when an HVC
> >> + * instruction is issued since all traps are disabled when running the host
> >> + * kernel as per the Hyp-mode initialization at boot time.
> >> + *
> >> + * HVC instructions cause a trap to the vector page + offset 0x18 (see hyp_hvc
> >> + * below) when the HVC instruction is called from SVC mode (i.e. a guest or the
> >> + * host kernel) and they cause a trap to the vector page + offset 0xc when HVC
> >> + * instructions are called from within Hyp-mode.
> >> + *
> >> + * Hyp-ABI: Calling HYP-mode functions from host (in SVC mode):
> >> + *    Switching to Hyp mode is done through a simple HVC #0 instruction. The
> >> + *    exception vector code will check that the HVC comes from VMID==0 and if
> >> + *    so will push the necessary state (SPSR, lr_usr) on the Hyp stack.
> >> + *    - r0 contains a pointer to a HYP function
> >> + *    - r1, r2, and r3 contain arguments to the above function.
> >> + *    - The HYP function will be called with its arguments in r0, r1 and r2.
> >> + *    On HYP function return, we return directly to SVC.
> >> + *
> >> + * Note that the above is used to execute code in Hyp-mode from a host-kernel
> >> + * point of view, and is a different concept from performing a world-switch and
> >> + * executing guest code SVC mode (with a VMID != 0).
> >>   */
> >>
> >> +/* Handle undef, svc, pabt, or dabt by crashing with a user notice */
> >> +.macro bad_exception exception_code, panic_str
> >> +     push    {r0-r2}
> >> +     mrrc    p15, 6, r0, r1, c2      @ Read VTTBR
> >> +     lsr     r1, r1, #16
> >> +     ands    r1, r1, #0xff
> >> +     beq     99f
> >> +
> >> +     load_vcpu                       @ Load VCPU pointer
> >> +     .if \exception_code == ARM_EXCEPTION_DATA_ABORT
> >> +     mrc     p15, 4, r2, c5, c2, 0   @ HSR
> >> +     mrc     p15, 4, r1, c6, c0, 0   @ HDFAR
> >> +     str     r2, [vcpu, #VCPU_HSR]
> >> +     str     r1, [vcpu, #VCPU_HxFAR]
> >> +     .endif
> >> +     .if \exception_code == ARM_EXCEPTION_PREF_ABORT
> >> +     mrc     p15, 4, r2, c5, c2, 0   @ HSR
> >> +     mrc     p15, 4, r1, c6, c0, 2   @ HIFAR
> >> +     str     r2, [vcpu, #VCPU_HSR]
> >> +     str     r1, [vcpu, #VCPU_HxFAR]
> >> +     .endif
> >> +     mov     r1, #\exception_code
> >> +     b       __kvm_vcpu_return
> >> +
> >> +     @ We were in the host already. Let's craft a panic-ing return to SVC.
> >> +99:  mrs     r2, cpsr
> >> +     bic     r2, r2, #MODE_MASK
> >> +     orr     r2, r2, #SVC_MODE
> >> +THUMB(       orr     r2, r2, #PSR_T_BIT      )
> >> +     msr     spsr_cxsf, r2
> >> +     mrs     r1, ELR_hyp
> >> +     ldr     r2, =BSYM(panic)
> >> +     msr     ELR_hyp, r2
> >> +     ldr     r0, =\panic_str
> >> +     eret
> >> +.endm
> >> +
> >> +     .text
> >> +
> >>       .align 5
> >>  __kvm_hyp_vector:
> >>       .globl __kvm_hyp_vector
> >> -     nop
> >> +
> >> +     @ Hyp-mode exception vector
> >> +     W(b)    hyp_reset
> >> +     W(b)    hyp_undef
> >> +     W(b)    hyp_svc
> >> +     W(b)    hyp_pabt
> >> +     W(b)    hyp_dabt
> >> +     W(b)    hyp_hvc
> >> +     W(b)    hyp_irq
> >> +     W(b)    hyp_fiq
> >> +
> >> +     .align
> >> +hyp_reset:
> >> +     b       hyp_reset
> >> +
> >> +     .align
> >> +hyp_undef:
> >> +     bad_exception ARM_EXCEPTION_UNDEFINED, und_die_str
> >> +
> >> +     .align
> >> +hyp_svc:
> >> +     bad_exception ARM_EXCEPTION_HVC, svc_die_str
> >> +
> >> +     .align
> >> +hyp_pabt:
> >> +     bad_exception ARM_EXCEPTION_PREF_ABORT, pabt_die_str
> >> +
> >> +     .align
> >> +hyp_dabt:
> >> +     bad_exception ARM_EXCEPTION_DATA_ABORT, dabt_die_str
> >> +
> >> +     .align
> >> +hyp_hvc:
> >> +     /*
> >> +      * Getting here is either becuase of a trap from a guest or from calling
> >> +      * HVC from the host kernel, which means "switch to Hyp mode".
> >> +      */
> >> +     push    {r0, r1, r2}
> >> +
> >> +     @ Check syndrome register
> >> +     mrc     p15, 4, r1, c5, c2, 0   @ HSR
> >> +     lsr     r0, r1, #HSR_EC_SHIFT
> >> +#ifdef CONFIG_VFPv3
> >> +     cmp     r0, #HSR_EC_CP_0_13
> >> +     beq     switch_to_guest_vfp
> >> +#endif
> >> +     cmp     r0, #HSR_EC_HVC
> >> +     bne     guest_trap              @ Not HVC instr.
> >> +
> >> +     /*
> >> +      * Let's check if the HVC came from VMID 0 and allow simple
> >> +      * switch to Hyp mode
> >> +      */
> >> +     mrrc    p15, 6, r0, r2, c2
> >> +     lsr     r2, r2, #16
> >> +     and     r2, r2, #0xff
> >> +     cmp     r2, #0
> >> +     bne     guest_trap              @ Guest called HVC
> >> +
> >> +host_switch_to_hyp:
> >> +     pop     {r0, r1, r2}
> >> +
> >> +     push    {lr}
> >> +     mrs     lr, SPSR
> >> +     push    {lr}
> >> +
> >> +     mov     lr, r0
> >> +     mov     r0, r1
> >> +     mov     r1, r2
> >> +     mov     r2, r3
> >> +
> >> +THUMB(       orr     lr, #1)
> >> +     blx     lr                      @ Call the HYP function
> >> +
> >> +     pop     {lr}
> >> +     msr     SPSR_csxf, lr
> >> +     pop     {lr}
> >> +     eret
> >> +
> >> +guest_trap:
> >> +     load_vcpu                       @ Load VCPU pointer to r0
> >> +     str     r1, [vcpu, #VCPU_HSR]
> >> +
> >> +     @ Check if we need the fault information
> >> +     lsr     r1, r1, #HSR_EC_SHIFT
> >> +     cmp     r1, #HSR_EC_IABT
> >> +     mrceq   p15, 4, r2, c6, c0, 2   @ HIFAR
> >> +     beq     2f
> >> +     cmp     r1, #HSR_EC_DABT
> >> +     bne     1f
> >> +     mrc     p15, 4, r2, c6, c0, 0   @ HDFAR
> >> +
> >> +2:   str     r2, [vcpu, #VCPU_HxFAR]
> >> +
> >> +     /*
> >> +      * B3.13.5 Reporting exceptions taken to the Non-secure PL2 mode:
> >> +      *
> >> +      * Abort on the stage 2 translation for a memory access from a
> >> +      * Non-secure PL1 or PL0 mode:
> >> +      *
> >> +      * For any Access flag fault or Translation fault, and also for any
> >> +      * Permission fault on the stage 2 translation of a memory access
> >> +      * made as part of a translation table walk for a stage 1 translation,
> >> +      * the HPFAR holds the IPA that caused the fault. Otherwise, the HPFAR
> >> +      * is UNKNOWN.
> >> +      */
> >> +
> >> +     /* Check for permission fault, and S1PTW */
> >> +     mrc     p15, 4, r1, c5, c2, 0   @ HSR
> >> +     and     r0, r1, #HSR_FSC_TYPE
> >> +     cmp     r0, #FSC_PERM
> >> +     tsteq   r1, #(1 << 7)           @ S1PTW
> >> +     mrcne   p15, 4, r2, c6, c0, 4   @ HPFAR
> >> +     bne     3f
> >> +
> >> +     /* Resolve IPA using the xFAR */
> >> +     mcr     p15, 0, r2, c7, c8, 0   @ ATS1CPR
> >> +     isb
> >> +     mrrc    p15, 0, r0, r1, c7      @ PAR
> >> +     tst     r0, #1
> >> +     bne     4f                      @ Failed translation
> >> +     ubfx    r2, r0, #12, #20
> >> +     lsl     r2, r2, #4
> >> +     orr     r2, r2, r1, lsl #24
> >> +
> >> +3:   load_vcpu                       @ Load VCPU pointer to r0
> >> +     str     r2, [r0, #VCPU_HPFAR]
> >> +
> >> +1:   mov     r1, #ARM_EXCEPTION_HVC
> >> +     b       __kvm_vcpu_return
> >> +
> >> +4:   pop     {r0, r1, r2}            @ Failed translation, return to guest
> >> +     eret
> >> +
> >> +/*
> >> + * If VFPv3 support is not available, then we will not switch the VFP
> >> + * registers; however cp10 and cp11 accesses will still trap and fallback
> >> + * to the regular coprocessor emulation code, which currently will
> >> + * inject an undefined exception to the guest.
> >> + */
> >> +#ifdef CONFIG_VFPv3
> >> +switch_to_guest_vfp:
> >> +     load_vcpu                       @ Load VCPU pointer to r0
> >> +     push    {r3-r7}
> >> +
> >> +     @ NEON/VFP used.  Turn on VFP access.
> >> +     set_hcptr vmexit, (HCPTR_TCP(10) | HCPTR_TCP(11))
> >> +
> >> +     @ Switch VFP/NEON hardware state to the guest's
> >> +     add     r7, r0, #VCPU_VFP_HOST
> >> +     ldr     r7, [r7]
> >> +     store_vfp_state r7
> >> +     add     r7, r0, #VCPU_VFP_GUEST
> >> +     restore_vfp_state r7
> >> +
> >> +     pop     {r3-r7}
> >> +     pop     {r0-r2}
> >> +     eret
> >> +#endif
> >> +
> >> +     .align
> >> +hyp_irq:
> >> +     push    {r0, r1, r2}
> >> +     mov     r1, #ARM_EXCEPTION_IRQ
> >> +     load_vcpu                       @ Load VCPU pointer to r0
> >> +     b       __kvm_vcpu_return
> >> +
> >> +     .align
> >> +hyp_fiq:
> >> +     b       hyp_fiq
> >> +
> >> +     .ltorg
> >>
> >>  __kvm_hyp_code_end:
> >>       .globl  __kvm_hyp_code_end
> >> +
> >> +     .section ".rodata"
> >> +
> >> +und_die_str:
> >> +     .ascii  "unexpected undefined exception in Hyp mode at: %#08x"
> >> +pabt_die_str:
> >> +     .ascii  "unexpected prefetch abort in Hyp mode at: %#08x"
> >> +dabt_die_str:
> >> +     .ascii  "unexpected data abort in Hyp mode at: %#08x"
> >> +svc_die_str:
> >> +     .ascii  "unexpected HVC/SVC trap in Hyp mode at: %#08x"
> >> diff --git a/arch/arm/kvm/interrupts_head.S b/arch/arm/kvm/interrupts_head.S
> >> new file mode 100644
> >> index 0000000..f59a580
> >> --- /dev/null
> >> +++ b/arch/arm/kvm/interrupts_head.S
> >> @@ -0,0 +1,443 @@
> >> +#define VCPU_USR_REG(_reg_nr)        (VCPU_USR_REGS + (_reg_nr * 4))
> >> +#define VCPU_USR_SP          (VCPU_USR_REG(13))
> >> +#define VCPU_USR_LR          (VCPU_USR_REG(14))
> >> +#define CP15_OFFSET(_cp15_reg_idx) (VCPU_CP15 + (_cp15_reg_idx * 4))
> >> +
> >> +/*
> >> + * Many of these macros need to access the VCPU structure, which is always
> >> + * held in r0. These macros should never clobber r1, as it is used to hold the
> >> + * exception code on the return path (except of course the macro that switches
> >> + * all the registers before the final jump to the VM).
> >> + */
> >> +vcpu .req    r0              @ vcpu pointer always in r0
> >> +
> >> +/* Clobbers {r2-r6} */
> >> +.macro store_vfp_state vfp_base
> >> +     @ The VFPFMRX and VFPFMXR macros are the VMRS and VMSR instructions
> >> +     VFPFMRX r2, FPEXC
> >> +     @ Make sure VFP is enabled so we can touch the registers.
> >> +     orr     r6, r2, #FPEXC_EN
> >> +     VFPFMXR FPEXC, r6
> >> +
> >> +     VFPFMRX r3, FPSCR
> >> +     tst     r2, #FPEXC_EX           @ Check for VFP Subarchitecture
> >> +     beq     1f
> >> +     @ If FPEXC_EX is 0, then FPINST/FPINST2 reads are upredictable, so
> >> +     @ we only need to save them if FPEXC_EX is set.
> >> +     VFPFMRX r4, FPINST
> >> +     tst     r2, #FPEXC_FP2V
> >> +     VFPFMRX r5, FPINST2, ne         @ vmrsne
> >> +     bic     r6, r2, #FPEXC_EX       @ FPEXC_EX disable
> >> +     VFPFMXR FPEXC, r6
> >> +1:
> >> +     VFPFSTMIA \vfp_base, r6         @ Save VFP registers
> >> +     stm     \vfp_base, {r2-r5}      @ Save FPEXC, FPSCR, FPINST, FPINST2
> >> +.endm
> >> +
> >> +/* Assume FPEXC_EN is on and FPEXC_EX is off, clobbers {r2-r6} */
> >> +.macro restore_vfp_state vfp_base
> >> +     VFPFLDMIA \vfp_base, r6         @ Load VFP registers
> >> +     ldm     \vfp_base, {r2-r5}      @ Load FPEXC, FPSCR, FPINST, FPINST2
> >> +
> >> +     VFPFMXR FPSCR, r3
> >> +     tst     r2, #FPEXC_EX           @ Check for VFP Subarchitecture
> >> +     beq     1f
> >> +     VFPFMXR FPINST, r4
> >> +     tst     r2, #FPEXC_FP2V
> >> +     VFPFMXR FPINST2, r5, ne
> >> +1:
> >> +     VFPFMXR FPEXC, r2       @ FPEXC (last, in case !EN)
> >> +.endm
> >> +
> >> +/* These are simply for the macros to work - value don't have meaning */
> >> +.equ usr, 0
> >> +.equ svc, 1
> >> +.equ abt, 2
> >> +.equ und, 3
> >> +.equ irq, 4
> >> +.equ fiq, 5
> >> +
> >> +.macro push_host_regs_mode mode
> >> +     mrs     r2, SP_\mode
> >> +     mrs     r3, LR_\mode
> >> +     mrs     r4, SPSR_\mode
> >> +     push    {r2, r3, r4}
> >> +.endm
> >> +
> >> +/*
> >> + * Store all host persistent registers on the stack.
> >> + * Clobbers all registers, in all modes, except r0 and r1.
> >> + */
> >> +.macro save_host_regs
> >> +     /* Hyp regs. Only ELR_hyp (SPSR_hyp already saved) */
> >> +     mrs     r2, ELR_hyp
> >> +     push    {r2}
> >> +
> >> +     /* usr regs */
> >> +     push    {r4-r12}        @ r0-r3 are always clobbered
> >> +     mrs     r2, SP_usr
> >> +     mov     r3, lr
> >> +     push    {r2, r3}
> >> +
> >> +     push_host_regs_mode svc
> >> +     push_host_regs_mode abt
> >> +     push_host_regs_mode und
> >> +     push_host_regs_mode irq
> >> +
> >> +     /* fiq regs */
> >> +     mrs     r2, r8_fiq
> >> +     mrs     r3, r9_fiq
> >> +     mrs     r4, r10_fiq
> >> +     mrs     r5, r11_fiq
> >> +     mrs     r6, r12_fiq
> >> +     mrs     r7, SP_fiq
> >> +     mrs     r8, LR_fiq
> >> +     mrs     r9, SPSR_fiq
> >> +     push    {r2-r9}
> >> +.endm
> >> +
> >> +.macro pop_host_regs_mode mode
> >> +     pop     {r2, r3, r4}
> >> +     msr     SP_\mode, r2
> >> +     msr     LR_\mode, r3
> >> +     msr     SPSR_\mode, r4
> >> +.endm
> >> +
> >> +/*
> >> + * Restore all host registers from the stack.
> >> + * Clobbers all registers, in all modes, except r0 and r1.
> >> + */
> >> +.macro restore_host_regs
> >> +     pop     {r2-r9}
> >> +     msr     r8_fiq, r2
> >> +     msr     r9_fiq, r3
> >> +     msr     r10_fiq, r4
> >> +     msr     r11_fiq, r5
> >> +     msr     r12_fiq, r6
> >> +     msr     SP_fiq, r7
> >> +     msr     LR_fiq, r8
> >> +     msr     SPSR_fiq, r9
> >> +
> >> +     pop_host_regs_mode irq
> >> +     pop_host_regs_mode und
> >> +     pop_host_regs_mode abt
> >> +     pop_host_regs_mode svc
> >> +
> >> +     pop     {r2, r3}
> >> +     msr     SP_usr, r2
> >> +     mov     lr, r3
> >> +     pop     {r4-r12}
> >> +
> >> +     pop     {r2}
> >> +     msr     ELR_hyp, r2
> >> +.endm
> >> +
> >> +/*
> >> + * Restore SP, LR and SPSR for a given mode. offset is the offset of
> >> + * this mode's registers from the VCPU base.
> >> + *
> >> + * Assumes vcpu pointer in vcpu reg
> >> + *
> >> + * Clobbers r1, r2, r3, r4.
> >> + */
> >> +.macro restore_guest_regs_mode mode, offset
> >> +     add     r1, vcpu, \offset
> >> +     ldm     r1, {r2, r3, r4}
> >> +     msr     SP_\mode, r2
> >> +     msr     LR_\mode, r3
> >> +     msr     SPSR_\mode, r4
> >> +.endm
> >> +
> >> +/*
> >> + * Restore all guest registers from the vcpu struct.
> >> + *
> >> + * Assumes vcpu pointer in vcpu reg
> >> + *
> >> + * Clobbers *all* registers.
> >> + */
> >> +.macro restore_guest_regs
> >> +     restore_guest_regs_mode svc, #VCPU_SVC_REGS
> >> +     restore_guest_regs_mode abt, #VCPU_ABT_REGS
> >> +     restore_guest_regs_mode und, #VCPU_UND_REGS
> >> +     restore_guest_regs_mode irq, #VCPU_IRQ_REGS
> >> +
> >> +     add     r1, vcpu, #VCPU_FIQ_REGS
> >> +     ldm     r1, {r2-r9}
> >> +     msr     r8_fiq, r2
> >> +     msr     r9_fiq, r3
> >> +     msr     r10_fiq, r4
> >> +     msr     r11_fiq, r5
> >> +     msr     r12_fiq, r6
> >> +     msr     SP_fiq, r7
> >> +     msr     LR_fiq, r8
> >> +     msr     SPSR_fiq, r9
> >> +
> >> +     @ Load return state
> >> +     ldr     r2, [vcpu, #VCPU_PC]
> >> +     ldr     r3, [vcpu, #VCPU_CPSR]
> >> +     msr     ELR_hyp, r2
> >> +     msr     SPSR_cxsf, r3
> >> +
> >> +     @ Load user registers
> >> +     ldr     r2, [vcpu, #VCPU_USR_SP]
> >> +     ldr     r3, [vcpu, #VCPU_USR_LR]
> >> +     msr     SP_usr, r2
> >> +     mov     lr, r3
> >> +     add     vcpu, vcpu, #(VCPU_USR_REGS)
> >> +     ldm     vcpu, {r0-r12}
> >> +.endm
> >> +
> >> +/*
> >> + * Save SP, LR and SPSR for a given mode. offset is the offset of
> >> + * this mode's registers from the VCPU base.
> >> + *
> >> + * Assumes vcpu pointer in vcpu reg
> >> + *
> >> + * Clobbers r2, r3, r4, r5.
> >> + */
> >> +.macro save_guest_regs_mode mode, offset
> >> +     add     r2, vcpu, \offset
> >> +     mrs     r3, SP_\mode
> >> +     mrs     r4, LR_\mode
> >> +     mrs     r5, SPSR_\mode
> >> +     stm     r2, {r3, r4, r5}
> >> +.endm
> >> +
> >> +/*
> >> + * Save all guest registers to the vcpu struct
> >> + * Expects guest's r0, r1, r2 on the stack.
> >> + *
> >> + * Assumes vcpu pointer in vcpu reg
> >> + *
> >> + * Clobbers r2, r3, r4, r5.
> >> + */
> >> +.macro save_guest_regs
> >> +     @ Store usr registers
> >> +     add     r2, vcpu, #VCPU_USR_REG(3)
> >> +     stm     r2, {r3-r12}
> >> +     add     r2, vcpu, #VCPU_USR_REG(0)
> >> +     pop     {r3, r4, r5}            @ r0, r1, r2
> >> +     stm     r2, {r3, r4, r5}
> >> +     mrs     r2, SP_usr
> >> +     mov     r3, lr
> >> +     str     r2, [vcpu, #VCPU_USR_SP]
> >> +     str     r3, [vcpu, #VCPU_USR_LR]
> >> +
> >> +     @ Store return state
> >> +     mrs     r2, ELR_hyp
> >> +     mrs     r3, spsr
> >> +     str     r2, [vcpu, #VCPU_PC]
> >> +     str     r3, [vcpu, #VCPU_CPSR]
> >> +
> >> +     @ Store other guest registers
> >> +     save_guest_regs_mode svc, #VCPU_SVC_REGS
> >> +     save_guest_regs_mode abt, #VCPU_ABT_REGS
> >> +     save_guest_regs_mode und, #VCPU_UND_REGS
> >> +     save_guest_regs_mode irq, #VCPU_IRQ_REGS
> >> +.endm
> >> +
> >> +/* Reads cp15 registers from hardware and stores them in memory
> >> + * @store_to_vcpu: If 0, registers are written in-order to the stack,
> >> + *              otherwise to the VCPU struct pointed to by vcpup
> >> + *
> >> + * Assumes vcpu pointer in vcpu reg
> >> + *
> >> + * Clobbers r2 - r12
> >> + */
> >> +.macro read_cp15_state store_to_vcpu
> >> +     mrc     p15, 0, r2, c1, c0, 0   @ SCTLR
> >> +     mrc     p15, 0, r3, c1, c0, 2   @ CPACR
> >> +     mrc     p15, 0, r4, c2, c0, 2   @ TTBCR
> >> +     mrc     p15, 0, r5, c3, c0, 0   @ DACR
> >> +     mrrc    p15, 0, r6, r7, c2      @ TTBR 0
> >> +     mrrc    p15, 1, r8, r9, c2      @ TTBR 1
> >> +     mrc     p15, 0, r10, c10, c2, 0 @ PRRR
> >> +     mrc     p15, 0, r11, c10, c2, 1 @ NMRR
> >> +     mrc     p15, 2, r12, c0, c0, 0  @ CSSELR
> >> +
> >> +     .if \store_to_vcpu == 0
> >> +     push    {r2-r12}                @ Push CP15 registers
> >> +     .else
> >> +     str     r2, [vcpu, #CP15_OFFSET(c1_SCTLR)]
> >> +     str     r3, [vcpu, #CP15_OFFSET(c1_CPACR)]
> >> +     str     r4, [vcpu, #CP15_OFFSET(c2_TTBCR)]
> >> +     str     r5, [vcpu, #CP15_OFFSET(c3_DACR)]
> >> +     add     vcpu, vcpu, #CP15_OFFSET(c2_TTBR0)
> >> +     strd    r6, r7, [vcpu]
> >> +     add     vcpu, vcpu, #CP15_OFFSET(c2_TTBR1) - CP15_OFFSET(c2_TTBR0)
> >> +     strd    r8, r9, [vcpu]
> >> +     sub     vcpu, vcpu, #CP15_OFFSET(c2_TTBR1)
> >> +     str     r10, [vcpu, #CP15_OFFSET(c10_PRRR)]
> >> +     str     r11, [vcpu, #CP15_OFFSET(c10_NMRR)]
> >> +     str     r12, [vcpu, #CP15_OFFSET(c0_CSSELR)]
> >> +     .endif
> >> +
> >> +     mrc     p15, 0, r2, c13, c0, 1  @ CID
> >> +     mrc     p15, 0, r3, c13, c0, 2  @ TID_URW
> >> +     mrc     p15, 0, r4, c13, c0, 3  @ TID_URO
> >> +     mrc     p15, 0, r5, c13, c0, 4  @ TID_PRIV
> >> +     mrc     p15, 0, r6, c5, c0, 0   @ DFSR
> >> +     mrc     p15, 0, r7, c5, c0, 1   @ IFSR
> >> +     mrc     p15, 0, r8, c5, c1, 0   @ ADFSR
> >> +     mrc     p15, 0, r9, c5, c1, 1   @ AIFSR
> >> +     mrc     p15, 0, r10, c6, c0, 0  @ DFAR
> >> +     mrc     p15, 0, r11, c6, c0, 2  @ IFAR
> >> +     mrc     p15, 0, r12, c12, c0, 0 @ VBAR
> >> +
> >> +     .if \store_to_vcpu == 0
> >> +     push    {r2-r12}                @ Push CP15 registers
> >> +     .else
> >> +     str     r2, [vcpu, #CP15_OFFSET(c13_CID)]
> >> +     str     r3, [vcpu, #CP15_OFFSET(c13_TID_URW)]
> >> +     str     r4, [vcpu, #CP15_OFFSET(c13_TID_URO)]
> >> +     str     r5, [vcpu, #CP15_OFFSET(c13_TID_PRIV)]
> >> +     str     r6, [vcpu, #CP15_OFFSET(c5_DFSR)]
> >> +     str     r7, [vcpu, #CP15_OFFSET(c5_IFSR)]
> >> +     str     r8, [vcpu, #CP15_OFFSET(c5_ADFSR)]
> >> +     str     r9, [vcpu, #CP15_OFFSET(c5_AIFSR)]
> >> +     str     r10, [vcpu, #CP15_OFFSET(c6_DFAR)]
> >> +     str     r11, [vcpu, #CP15_OFFSET(c6_IFAR)]
> >> +     str     r12, [vcpu, #CP15_OFFSET(c12_VBAR)]
> >> +     .endif
> >> +.endm
> >> +
> >> +/*
> >> + * Reads cp15 registers from memory and writes them to hardware
> >> + * @read_from_vcpu: If 0, registers are read in-order from the stack,
> >> + *               otherwise from the VCPU struct pointed to by vcpup
> >> + *
> >> + * Assumes vcpu pointer in vcpu reg
> >> + */
> >> +.macro write_cp15_state read_from_vcpu
> >> +     .if \read_from_vcpu == 0
> >> +     pop     {r2-r12}
> >> +     .else
> >> +     ldr     r2, [vcpu, #CP15_OFFSET(c13_CID)]
> >> +     ldr     r3, [vcpu, #CP15_OFFSET(c13_TID_URW)]
> >> +     ldr     r4, [vcpu, #CP15_OFFSET(c13_TID_URO)]
> >> +     ldr     r5, [vcpu, #CP15_OFFSET(c13_TID_PRIV)]
> >> +     ldr     r6, [vcpu, #CP15_OFFSET(c5_DFSR)]
> >> +     ldr     r7, [vcpu, #CP15_OFFSET(c5_IFSR)]
> >> +     ldr     r8, [vcpu, #CP15_OFFSET(c5_ADFSR)]
> >> +     ldr     r9, [vcpu, #CP15_OFFSET(c5_AIFSR)]
> >> +     ldr     r10, [vcpu, #CP15_OFFSET(c6_DFAR)]
> >> +     ldr     r11, [vcpu, #CP15_OFFSET(c6_IFAR)]
> >> +     ldr     r12, [vcpu, #CP15_OFFSET(c12_VBAR)]
> >> +     .endif
> >> +
> >> +     mcr     p15, 0, r2, c13, c0, 1  @ CID
> >> +     mcr     p15, 0, r3, c13, c0, 2  @ TID_URW
> >> +     mcr     p15, 0, r4, c13, c0, 3  @ TID_URO
> >> +     mcr     p15, 0, r5, c13, c0, 4  @ TID_PRIV
> >> +     mcr     p15, 0, r6, c5, c0, 0   @ DFSR
> >> +     mcr     p15, 0, r7, c5, c0, 1   @ IFSR
> >> +     mcr     p15, 0, r8, c5, c1, 0   @ ADFSR
> >> +     mcr     p15, 0, r9, c5, c1, 1   @ AIFSR
> >> +     mcr     p15, 0, r10, c6, c0, 0  @ DFAR
> >> +     mcr     p15, 0, r11, c6, c0, 2  @ IFAR
> >> +     mcr     p15, 0, r12, c12, c0, 0 @ VBAR
> >> +
> >> +     .if \read_from_vcpu == 0
> >> +     pop     {r2-r12}
> >> +     .else
> >> +     ldr     r2, [vcpu, #CP15_OFFSET(c1_SCTLR)]
> >> +     ldr     r3, [vcpu, #CP15_OFFSET(c1_CPACR)]
> >> +     ldr     r4, [vcpu, #CP15_OFFSET(c2_TTBCR)]
> >> +     ldr     r5, [vcpu, #CP15_OFFSET(c3_DACR)]
> >> +     add     vcpu, vcpu, #CP15_OFFSET(c2_TTBR0)
> >> +     ldrd    r6, r7, [vcpu]
> >> +     add     vcpu, vcpu, #CP15_OFFSET(c2_TTBR1) - CP15_OFFSET(c2_TTBR0)
> >> +     ldrd    r8, r9, [vcpu]
> >> +     sub     vcpu, vcpu, #CP15_OFFSET(c2_TTBR1)
> >> +     ldr     r10, [vcpu, #CP15_OFFSET(c10_PRRR)]
> >> +     ldr     r11, [vcpu, #CP15_OFFSET(c10_NMRR)]
> >> +     ldr     r12, [vcpu, #CP15_OFFSET(c0_CSSELR)]
> >> +     .endif
> >> +
> >> +     mcr     p15, 0, r2, c1, c0, 0   @ SCTLR
> >> +     mcr     p15, 0, r3, c1, c0, 2   @ CPACR
> >> +     mcr     p15, 0, r4, c2, c0, 2   @ TTBCR
> >> +     mcr     p15, 0, r5, c3, c0, 0   @ DACR
> >> +     mcrr    p15, 0, r6, r7, c2      @ TTBR 0
> >> +     mcrr    p15, 1, r8, r9, c2      @ TTBR 1
> >> +     mcr     p15, 0, r10, c10, c2, 0 @ PRRR
> >> +     mcr     p15, 0, r11, c10, c2, 1 @ NMRR
> >> +     mcr     p15, 2, r12, c0, c0, 0  @ CSSELR
> >> +.endm
> >> +
> >> +/*
> >> + * Save the VGIC CPU state into memory
> >> + *
> >> + * Assumes vcpu pointer in vcpu reg
> >> + */
> >> +.macro save_vgic_state
> >> +.endm
> >> +
> >> +/*
> >> + * Restore the VGIC CPU state from memory
> >> + *
> >> + * Assumes vcpu pointer in vcpu reg
> >> + */
> >> +.macro restore_vgic_state
> >> +.endm
> >> +
> >> +.equ vmentry,        0
> >> +.equ vmexit, 1
> >> +
> >> +/* Configures the HSTR (Hyp System Trap Register) on entry/return
> >> + * (hardware reset value is 0) */
> >> +.macro set_hstr operation
> >> +     mrc     p15, 4, r2, c1, c1, 3
> >> +     ldr     r3, =HSTR_T(15)
> >> +     .if \operation == vmentry
> >> +     orr     r2, r2, r3              @ Trap CR{15}
> >> +     .else
> >> +     bic     r2, r2, r3              @ Don't trap any CRx accesses
> >> +     .endif
> >> +     mcr     p15, 4, r2, c1, c1, 3
> >> +.endm
> >> +
> >> +/* Configures the HCPTR (Hyp Coprocessor Trap Register) on entry/return
> >> + * (hardware reset value is 0). Keep previous value in r2. */
> >> +.macro set_hcptr operation, mask
> >> +     mrc     p15, 4, r2, c1, c1, 2
> >> +     ldr     r3, =\mask
> >> +     .if \operation == vmentry
> >> +     orr     r3, r2, r3              @ Trap coproc-accesses defined in mask
> >> +     .else
> >> +     bic     r3, r2, r3              @ Don't trap defined coproc-accesses
> >> +     .endif
> >> +     mcr     p15, 4, r3, c1, c1, 2
> >> +.endm
> >> +
> >> +/* Configures the HDCR (Hyp Debug Configuration Register) on entry/return
> >> + * (hardware reset value is 0) */
> >> +.macro set_hdcr operation
> >> +     mrc     p15, 4, r2, c1, c1, 1
> >> +     ldr     r3, =(HDCR_TPM|HDCR_TPMCR)
> >> +     .if \operation == vmentry
> >> +     orr     r2, r2, r3              @ Trap some perfmon accesses
> >> +     .else
> >> +     bic     r2, r2, r3              @ Don't trap any perfmon accesses
> >> +     .endif
> >> +     mcr     p15, 4, r2, c1, c1, 1
> >> +.endm
> >> +
> >> +/* Enable/Disable: stage-2 trans., trap interrupts, trap wfi, trap smc */
> >> +.macro configure_hyp_role operation
> >> +     mrc     p15, 4, r2, c1, c1, 0   @ HCR
> >> +     bic     r2, r2, #HCR_VIRT_EXCP_MASK
> >> +     ldr     r3, =HCR_GUEST_MASK
> >> +     .if \operation == vmentry
> >> +     orr     r2, r2, r3
> >> +     ldr     r3, [vcpu, #VCPU_IRQ_LINES]
> > irq_lines are accessed atomically from vcpu_interrupt_line(), but there
> > is no memory barriers or atomic operations here. Looks suspicious though
> > I am not familiar with ARM memory model. As far as I understand
> > different translation regimes are used to access this memory, so who
> > knows what this does to access ordering.
> >
> >
> 
> there's an exception taken to switch to Hyp mode, which I'm quite sure
> implies a memory barrier.
> 
> >> +     orr     r2, r2, r3
> >> +     .else
> >> +     bic     r2, r2, r3
> >> +     .endif
> >> +     mcr     p15, 4, r2, c1, c1, 0
> >> +.endm
> >> +
> >> +.macro load_vcpu
> >> +     mrc     p15, 4, vcpu, c13, c0, 2        @ HTPIDR
> >> +.endm
> >>
> >> --
> >> To unsubscribe from this list: send the line "unsubscribe kvm" in
> >> the body of a message to majordomo at vger.kernel.org
> >> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >
> 
> commit e290b507f0d31c895bd515d69c0c2b50d76b20db
> Author: Christoffer Dall <[email-masked]>
> Date:   Tue Jan 15 20:53:03 2013 -0500
> 
>     KVM: ARM: Honor vcpu->requests in the world-switch code
> 
>     Honor vpuc->request by checking them accordingly and explicitly raise an
>     error if unsupported requests are set (we don't support any requests on
>     ARM currently).
> 
>     Also add some commenting to explain the synchronization in more details
>     here.  The commenting implied renaming a variable and changing error
>     handling slightly to improve readibility.
> 
>     Signed-off-by: Christoffer Dall <[email-masked]>
> 
> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> index 6ff5337..b23a709 100644
> --- a/arch/arm/kvm/arm.c
> +++ b/arch/arm/kvm/arm.c
> @@ -620,7 +620,7 @@ static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu)
>   */
>  int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  {
> -	int ret;
> +	int guest_ret, ret;
>  	sigset_t sigsaved;
> 
>  	/* Make sure they initialize the vcpu with KVM_ARM_VCPU_INIT */
> @@ -640,9 +640,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu,
> struct kvm_run *run)
>  	if (vcpu->sigset_active)
>  		sigprocmask(SIG_SETMASK, &vcpu->sigset, &sigsaved);
> 
> -	ret = 1;
>  	run->exit_reason = KVM_EXIT_UNKNOWN;
> -	while (ret > 0) {
> +	for (;;) {
>  		/*
>  		 * Check conditions before entering the guest
>  		 */
> @@ -650,18 +649,44 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu
> *vcpu, struct kvm_run *run)
> 
>  		update_vttbr(vcpu->kvm);
> 
> +		/*
> +		 * There is a dependency between setting IN_GUEST_MODE and
> +		 * sending requests.  We need to ensure:
> +		 *   1. Setting IN_GUEST_MODE before checking vcpu->requests.
> +		 *   2. We need to check vcpu_request after disabling IRQs
> +		 *      (see comment about signal_pending below).
> +		 */
> +		vcpu->mode = IN_GUEST_MODE;
> +
>  		local_irq_disable();
> 
>  		/*
> -		 * Re-check atomic conditions
> +		 * We need to be careful to check these variables after
> +		 * disabling interrupts.  For example with signals:
> +		 *   1. If the signal comes before the signal_pending check,
> +		 *      we will return to user space and everything's good.
> +		 *   2. If the signal comes after the signal_pending check,
> +		 *      we rely on an IPI to exit the guest and continue the
> +		 *      while loop, which checks for pending signals again.
>  		 */
>  		if (signal_pending(current)) {
>  			ret = -EINTR;
>  			run->exit_reason = KVM_EXIT_INTR;
> +			local_irq_enable();
> +			vcpu->mode = OUTSIDE_GUEST_MODE;
> +			break;
>  		}
> 
> -		if (ret <= 0 || need_new_vmid_gen(vcpu->kvm)) {
> +		if (vcpu->requests) {
> +			ret = -ENOSYS; /* requests not supported */
>  			local_irq_enable();
> +			vcpu->mode = OUTSIDE_GUEST_MODE;
> +			break;
> +		}
> +
> +		if (need_new_vmid_gen(vcpu->kvm)) {
> +			local_irq_enable();
> +			vcpu->mode = OUTSIDE_GUEST_MODE;
>  			continue;
>  		}
> 
> @@ -670,17 +695,15 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu
> *vcpu, struct kvm_run *run)
>  		 */
>  		trace_kvm_entry(*vcpu_pc(vcpu));
>  		kvm_guest_enter();
> -		vcpu->mode = IN_GUEST_MODE;
> 
>  		smp_mb(); /* set mode before reading vcpu->arch.pause */
>  		if (unlikely(vcpu->arch.pause)) {
>  			/* This means ignore, try again. */
> -			ret = ARM_EXCEPTION_IRQ;
> +			guest_ret = ARM_EXCEPTION_IRQ;
>  		} else {
> -			ret = kvm_call_hyp(__kvm_vcpu_run, vcpu);
> +			guest_ret = kvm_call_hyp(__kvm_vcpu_run, vcpu);
>  		}
> 
> -		vcpu->mode = OUTSIDE_GUEST_MODE;
>  		vcpu->arch.last_pcpu = smp_processor_id();
>  		kvm_guest_exit();
>  		trace_kvm_exit(*vcpu_pc(vcpu));
> @@ -695,12 +718,15 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu
> *vcpu, struct kvm_run *run)
>  		 * mode this time.
>  		 */
>  		local_irq_enable();
> +		vcpu->mode = OUTSIDE_GUEST_MODE;
> 
>  		/*
>  		 * Back from guest
>  		 *************************************************************/
> 
> -		ret = handle_exit(vcpu, run, ret);
> +		ret = handle_exit(vcpu, run, guest_ret);
> +		if (ret <= 0)
> +			break;
>  	}
> 
>  	if (vcpu->sigset_active)
> 
> commit fc9a9c5e9dd4eba4acd6bea5c8c083a9a854d662
> Author: Christoffer Dall <[email-masked]>
> Date:   Tue Jan 15 20:42:15 2013 -0500
> 
>     KVM: ARM: Remove unused memslot parameter
> 
> diff --git a/arch/arm/include/asm/kvm_mmio.h b/arch/arm/include/asm/kvm_mmio.h
> index 31ab9f5..571ccf0 100644
> --- a/arch/arm/include/asm/kvm_mmio.h
> +++ b/arch/arm/include/asm/kvm_mmio.h
> @@ -46,6 +46,6 @@ static inline void kvm_prepare_mmio(struct kvm_run *run,
> 
>  int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run);
>  int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
> -		 phys_addr_t fault_ipa, struct kvm_memory_slot *memslot);
> +		 phys_addr_t fault_ipa);
> 
>  #endif	/* __ARM_KVM_MMIO_H__ */
> diff --git a/arch/arm/kvm/mmio.c b/arch/arm/kvm/mmio.c
> index d6a4ca0..f655088 100644
> --- a/arch/arm/kvm/mmio.c
> +++ b/arch/arm/kvm/mmio.c
> @@ -117,7 +117,7 @@ static int decode_hsr(struct kvm_vcpu *vcpu,
> phys_addr_t fault_ipa,
>  }
> 
>  int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
> -		 phys_addr_t fault_ipa, struct kvm_memory_slot *memslot)
> +		 phys_addr_t fault_ipa)
>  {
>  	struct kvm_exit_mmio mmio;
>  	unsigned long rt;
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index 2a83ac9..c806080 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -588,7 +588,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu,
> struct kvm_run *run)
>  	unsigned long hsr_ec;
>  	unsigned long fault_status;
>  	phys_addr_t fault_ipa;
> -	struct kvm_memory_slot *memslot = NULL;
> +	struct kvm_memory_slot *memslot;
>  	bool is_iabt;
>  	gfn_t gfn;
>  	int ret;
> @@ -624,7 +624,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu,
> struct kvm_run *run)
> 
>  		/* Adjust page offset */
>  		fault_ipa |= vcpu->arch.hxfar & ~PAGE_MASK;
> -		return io_mem_abort(vcpu, run, fault_ipa, memslot);
> +		return io_mem_abort(vcpu, run, fault_ipa);
>  	}
> 
>  	memslot = gfn_to_memslot(vcpu->kvm, gfn);
> 
> commit 70667a06e445e240fb5e6352ccdc4bc8a290866e
> Author: Christoffer Dall <[email-masked]>
> Date:   Tue Jan 15 20:51:42 2013 -0500
> 
>     KVM: ARM: Grab kvm->srcu lock when handling page faults
> 
>     The memslots data structure is protected with an SRCU lock, so we should
>     grab the read side lock before traversing this data structure.
> 
>     Signed-off-by: Christoffer Dall <[email-masked]>
> 
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index c806080..0b7eabf 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -591,7 +591,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu,
> struct kvm_run *run)
>  	struct kvm_memory_slot *memslot;
>  	bool is_iabt;
>  	gfn_t gfn;
> -	int ret;
> +	int ret, idx;
> 
>  	hsr_ec = vcpu->arch.hsr >> HSR_EC_SHIFT;
>  	is_iabt = (hsr_ec == HSR_EC_IABT);
> @@ -627,13 +627,17 @@ int kvm_handle_guest_abort(struct kvm_vcpu
> *vcpu, struct kvm_run *run)
>  		return io_mem_abort(vcpu, run, fault_ipa);
>  	}
> 
> +	idx = srcu_read_lock(&vcpu->kvm->srcu);
>  	memslot = gfn_to_memslot(vcpu->kvm, gfn);
>  	if (!memslot->user_alloc) {
>  		kvm_err("non user-alloc memslots not supported\n");
> -		return -EINVAL;
> +		ret = -EINVAL;
> +		goto out_unlock;
>  	}
> 
>  	ret = user_mem_abort(vcpu, fault_ipa, gfn, memslot, fault_status);
> +out_unlock:
> +	srcu_read_unlock(&vcpu->kvm->srcu, idx);
>  	return ret ? ret : 1;
>  }
> 
> --
> 
> Thanks,
> -Christoffer

--
			Gleb.