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SubjectRe: [PATCH] KVM: x86: check for interrupts before deciding whether to exit the fast path
On Wed, Oct 20, 2021, Paolo Bonzini wrote:
> The kvm_x86_sync_pir_to_irr callback can sometimes set KVM_REQ_EVENT.
> If that happens exactly at the time that an exit is handled as
> EXIT_FASTPATH_REENTER_GUEST, vcpu_enter_guest will go incorrectly
> through the loop that calls kvm_x86_run, instead of processing
> the request promptly.
>
> Fixes: 379a3c8ee444 ("KVM: VMX: Optimize posted-interrupt delivery for timer fastpath")
> Cc: stable@vger.kernel.org
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---

Reviewed-by: Sean Christopherson <seanjc@google.com>

> arch/x86/kvm/x86.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index fa48948b4934..b9b31e5f72b0 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9781,14 +9781,14 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> if (likely(exit_fastpath != EXIT_FASTPATH_REENTER_GUEST))
> break;
>
> - if (unlikely(kvm_vcpu_exit_request(vcpu))) {
> + if (vcpu->arch.apicv_active)
> + static_call(kvm_x86_sync_pir_to_irr)(vcpu);
> +
> + if (unlikely(kvm_vcpu_exit_request(vcpu))) {
> exit_fastpath = EXIT_FASTPATH_EXIT_HANDLED;
> break;
> }
> -
> - if (vcpu->arch.apicv_active)
> - static_call(kvm_x86_sync_pir_to_irr)(vcpu);
> - }
> + }

I think someone working on git has a meta-entry in the obfuscated C context.
This is the most convoluted diff possible for a simple code move :-)

> /*
> * Do this here before restoring debug registers on the host. And
> --
> 2.27.0
>

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