[PATCH] KVM: arm64: Don't miss pending interrupts for suspended vCPU

[PATCH] KVM: arm64: Don't miss pending interrupts for suspended vCPU

[Oliver Upton]

In order to properly emulate the WFI instruction, KVM reads back
ICH_VMCR_EL2 and enables doorbells for GICv4. These preparations are
necessary in order to recognize pending interrupts in
kvm_arch_vcpu_runnable() and return to the guest. Until recently, this
work was done by kvm_arch_vcpu_{blocking,unblocking}(). Since commit
6109c5a6ab7f ("KVM: arm64: Move vGIC v4 handling for WFI out arch
callback hook"), these callbacks were gutted and superseded by
kvm_vcpu_wfi().

It is important to note that KVM implements PSCI CPU_SUSPEND calls as
a WFI within the guest. However, the implementation calls directly into
kvm_vcpu_halt(), which skips the needed work done in kvm_vcpu_wfi()
to detect pending interrupts. Fix the issue by calling the WFI helper.

Fixes: 6109c5a6ab7f ("KVM: arm64: Move vGIC v4 handling for WFI out arch callback hook")
Signed-off-by: Oliver Upton <oupton@google.com>
---
 arch/arm64/kvm/psci.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/psci.c b/arch/arm64/kvm/psci.c
index 3eae32876897..2ce60fecd861 100644
--- a/arch/arm64/kvm/psci.c
+++ b/arch/arm64/kvm/psci.c
@@ -46,8 +46,7 @@ static unsigned long kvm_psci_vcpu_suspend(struct kvm_vcpu *vcpu)
 	 * specification (ARM DEN 0022A). This means all suspend states
 	 * for KVM will preserve the register state.
 	 */
-	kvm_vcpu_halt(vcpu);
-	kvm_clear_request(KVM_REQ_UNHALT, vcpu);
+	kvm_vcpu_wfi(vcpu);
 
 	return PSCI_RET_SUCCESS;
 }
-- 
2.35.1.265.g69c8d7142f-goog


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Re: [PATCH] KVM: arm64: Don't miss pending interrupts for suspended vCPU

[Marc Zyngier]

On 2022-02-17 10:12, Oliver Upton wrote:
> In order to properly emulate the WFI instruction, KVM reads back
> ICH_VMCR_EL2 and enables doorbells for GICv4. These preparations are
> necessary in order to recognize pending interrupts in
> kvm_arch_vcpu_runnable() and return to the guest. Until recently, this
> work was done by kvm_arch_vcpu_{blocking,unblocking}(). Since commit
> 6109c5a6ab7f ("KVM: arm64: Move vGIC v4 handling for WFI out arch
> callback hook"), these callbacks were gutted and superseded by
> kvm_vcpu_wfi().
> 
> It is important to note that KVM implements PSCI CPU_SUSPEND calls as
> a WFI within the guest. However, the implementation calls directly into
> kvm_vcpu_halt(), which skips the needed work done in kvm_vcpu_wfi()
> to detect pending interrupts. Fix the issue by calling the WFI helper.
> 
> Fixes: 6109c5a6ab7f ("KVM: arm64: Move vGIC v4 handling for WFI out
> arch callback hook")
> Signed-off-by: Oliver Upton <oupton@google.com>
> ---
>  arch/arm64/kvm/psci.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kvm/psci.c b/arch/arm64/kvm/psci.c
> index 3eae32876897..2ce60fecd861 100644
> --- a/arch/arm64/kvm/psci.c
> +++ b/arch/arm64/kvm/psci.c
> @@ -46,8 +46,7 @@ static unsigned long kvm_psci_vcpu_suspend(struct
> kvm_vcpu *vcpu)
>  	 * specification (ARM DEN 0022A). This means all suspend states
>  	 * for KVM will preserve the register state.
>  	 */
> -	kvm_vcpu_halt(vcpu);
> -	kvm_clear_request(KVM_REQ_UNHALT, vcpu);
> +	kvm_vcpu_wfi(vcpu);
> 
>  	return PSCI_RET_SUCCESS;
>  }

Thanks for picking this up, I kept forgetting about fixing it.
I'll merge it once I'm back home.

         M.
-- 
Jazz is not dead. It just smells funny...

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Re: [PATCH] KVM: arm64: Don't miss pending interrupts for suspended vCPU

[Marc Zyngier]

On Thu, 17 Feb 2022 10:12:42 +0000, Oliver Upton wrote:
> In order to properly emulate the WFI instruction, KVM reads back
> ICH_VMCR_EL2 and enables doorbells for GICv4. These preparations are
> necessary in order to recognize pending interrupts in
> kvm_arch_vcpu_runnable() and return to the guest. Until recently, this
> work was done by kvm_arch_vcpu_{blocking,unblocking}(). Since commit
> 6109c5a6ab7f ("KVM: arm64: Move vGIC v4 handling for WFI out arch
> callback hook"), these callbacks were gutted and superseded by
> kvm_vcpu_wfi().
> 
> [...]

Applied to fixes, thanks!

[1/1] KVM: arm64: Don't miss pending interrupts for suspended vCPU
      commit: a867e9d0cc15039a6ef72e17e2603303dcd1783f

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