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 17:02:00 +0100

On Thu, Feb 22, 2018 at 03:01:17PM +0000, Marc Zyngier wrote:
> On Thu, 22 Feb 2018 14:42:27 +0000,
> Christoffer Dall wrote:
> > 
> > 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();
> > }
> 
> Yes. I think this would go a long way in making this code easy to
> understand. 

I'll give it a go on the next respin.

> It also mean that we can have a unified save/restore
> function that picks the right GIC back-end, resulting in less
> code duplication.
> 
Not sure I understand hat you mean here?

Thanks,
-Christoffer