linux-kernel - Re: [PATCH 1/5] KVM: x86: Re-enter guest if WRMSR(X2APIC

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Message-ID: <CABgObfYT_X3-Qjb_ouNAGX1OOL2ULT2aEA6SDKessSbJxGZEOQ@mail.gmail.com>
Date: Mon, 2 Sep 2024 11:58:40 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] KVM: x86: Re-enter guest if WRMSR(X2APIC_ICR)
 fastpath is successful

On Fri, Aug 2, 2024 at 9:51 PM Sean Christopherson <seanjc@...gle.com> wrote:
> Re-enter the guest in the fastpath if WRMSR emulation for x2APIC's ICR is
> successful, as no additional work is needed, i.e. there is no code unique
> for WRMSR exits between the fastpath and the "!= EXIT_FASTPATH_NONE" check
> in __vmx_handle_exit().

What about if you send an IPI to yourself?  Doesn't that return true
for kvm_vcpu_exit_request() if posted interrupts are disabled?

Paolo

> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/x86.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index af6c8cf6a37a..cf397110953f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2173,7 +2173,7 @@ fastpath_t handle_fastpath_set_msr_irqoff(struct kvm_vcpu *vcpu)
>                 data = kvm_read_edx_eax(vcpu);
>                 if (!handle_fastpath_set_x2apic_icr_irqoff(vcpu, data)) {
>                         kvm_skip_emulated_instruction(vcpu);
> -                       ret = EXIT_FASTPATH_EXIT_HANDLED;
> +                       ret = EXIT_FASTPATH_REENTER_GUEST;
>                 }
>                 break;
>         case MSR_IA32_TSC_DEADLINE:
> --
> 2.46.0.rc2.264.g509ed76dc8-goog
>