Subject: [PATCH v4 38/40] KVM: arm/arm64: Handle VGICv3 save/restore from the main VGIC code on VHE

From: [email-masked] (Christoffer Dall)
Date: Thu, 22 Feb 2018 15:42:27 +0100

On Thu, Feb 22, 2018 at 12:32:11PM +0000, Marc Zyngier wrote:
> On 15/02/18 21:03, Christoffer Dall wrote:
> > Just like we can program the GICv2 hypervisor control interface directly
> > from the core vgic code, we can do the same for the GICv3 hypervisor
> > control interface on VHE systems.
> > 
> > We do this by simply calling the save/restore functions when we have VHE
> > and we can then get rid of the save/restore function calls from the VHE
> > world switch function.
> > 
> > One caveat is that we now write GICv3 system register state before the
> > potential early exit path in the run loop, and because we sync back
> > state in the early exit path, we have to ensure that we read a
> > consistent GIC state from the sync path, even though we have never
> > actually run the guest with the newly written GIC state.  We solve this
> > by inserting an ISB in the early exit path.
> > 
> > Signed-off-by: Christoffer Dall <[email-masked]>
> > ---
> > 
> > Notes:
> >     Changes since v2:
> >      - Added ISB in the early exit path in the run loop as explained
> >        in the commit message.
> > 
> >  arch/arm64/kvm/hyp/switch.c | 3 ---
> >  virt/kvm/arm/arm.c          | 1 +
> >  virt/kvm/arm/vgic/vgic.c    | 5 +++++
> >  3 files changed, 6 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> > index cbafc27a617b..466cfcdbcaf3 100644
> > --- a/arch/arm64/kvm/hyp/switch.c
> > +++ b/arch/arm64/kvm/hyp/switch.c
> > @@ -399,8 +399,6 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
> >  	__activate_traps(vcpu);
> >  	__activate_vm(vcpu->kvm);
> >  
> > -	__vgic_restore_state(vcpu);
> > -
> >  	sysreg_restore_guest_state_vhe(guest_ctxt);
> >  	__debug_switch_to_guest(vcpu);
> >  
> > @@ -414,7 +412,6 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
> >  	fp_enabled = fpsimd_enabled_vhe();
> >  
> >  	sysreg_save_guest_state_vhe(guest_ctxt);
> > -	__vgic_save_state(vcpu);
> >  
> >  	__deactivate_traps(vcpu);
> >  
> > diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> > index 5bd879c78951..6de7641f3ff2 100644
> > --- a/virt/kvm/arm/arm.c
> > +++ b/virt/kvm/arm/arm.c
> > @@ -717,6 +717,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
> >  		if (ret <= 0 || need_new_vmid_gen(vcpu->kvm) ||
> >  		    kvm_request_pending(vcpu)) {
> >  			vcpu->mode = OUTSIDE_GUEST_MODE;
> > +			isb(); /* Ensure work in x_flush_hwstate is committed */
> >  			kvm_pmu_sync_hwstate(vcpu);
> >  			if (static_branch_unlikely(&userspace_irqchip_in_use))
> >  				kvm_timer_sync_hwstate(vcpu);
> > diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> > index 12e2a28f437e..d0a19a8c196a 100644
> > --- a/virt/kvm/arm/vgic/vgic.c
> > +++ b/virt/kvm/arm/vgic/vgic.c
> > @@ -19,6 +19,7 @@
> >  #include <linux/list_sort.h>
> >  #include <linux/interrupt.h>
> >  #include <linux/irq.h>
> > +#include <asm/kvm_hyp.h>
> >  
> >  #include "vgic.h"
> >  
> > @@ -753,6 +754,8 @@ static inline void vgic_save_state(struct kvm_vcpu *vcpu)
> >  {
> >  	if (!static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif))
> >  		vgic_v2_save_state(vcpu);
> > +	else if (has_vhe())
> > +		__vgic_v3_save_state(vcpu);
> >  }
> >  
> >  /* Sync back the hardware VGIC state into our emulation after a guest's run. */
> > @@ -777,6 +780,8 @@ static inline void vgic_restore_state(struct kvm_vcpu *vcpu)
> >  {
> >  	if (!static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif))
> >  		vgic_v2_restore_state(vcpu);
> > +	else if (has_vhe())
> > +		__vgic_v3_restore_state(vcpu);
> >  }
> >  
> >  /* Flush our emulation state into the GIC hardware before entering the guest. */
> > 
> 
> I'm slowly wrapping my brain around this thing again. If I grasp the
> general idea, we end up with two cases:
> 
> (1) The GIC is accessible from the kernel, and we save/restore it
> outside of the HYP code.
> 
> (2) The GIC is only accessible from the HYP code, and we do it there.
> 
> Maybe we should bite the bullet and introduce that primitive instead?
> 

You mean something the following?

static inline bool can_access_vgic_from_kernel(void)
{
	/*
	 * GICv2 can always be accessed from the kernel because it is
	 * memory-mapped, and VHE systems can access GICv3 EL2 system
	 * registers.
	 */
	return !static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif) || has_vhe();
}

Thanks,
-Christoffer