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Peter Anvin" , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , Thomas Gleixner , Vitaly Kuznetsov , Ingo Molnar Subject: Re: [PATCH 1/7] KVM: VMX: read idt_vectoring_info a bit earlier Message-ID: References: <20210217145718.1217358-1-mlevitsk@redhat.com> <20210217145718.1217358-2-mlevitsk@redhat.com> <09de977a-0275-0f4f-cf75-f45e4b5d9ca5@redhat.com> <666eb754189a380899b82e0a9798eb2560ae6972.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <666eb754189a380899b82e0a9798eb2560ae6972.camel@redhat.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, Feb 17, 2021, Maxim Levitsky wrote: > On Wed, 2021-02-17 at 17:06 +0100, Paolo Bonzini wrote: > > On 17/02/21 15:57, Maxim Levitsky wrote: > > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > > > index b3e36dc3f164..e428d69e21c0 100644 > > > --- a/arch/x86/kvm/vmx/vmx.c > > > +++ b/arch/x86/kvm/vmx/vmx.c > > > @@ -6921,13 +6921,15 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu) > > > if (unlikely((u16)vmx->exit_reason.basic == EXIT_REASON_MCE_DURING_VMENTRY)) > > > kvm_machine_check(); > > > > > > + if (likely(!vmx->exit_reason.failed_vmentry)) > > > + vmx->idt_vectoring_info = vmcs_read32(IDT_VECTORING_INFO_FIELD); > > > + > > > > Any reason for the if? > > Sean Christopherson asked me to do this to avoid updating idt_vectoring_info on failed > VM entry, to keep things as they were logically before this patch. Ya, specifically because the field isn't valid if VM-Enter fails. I'm also ok with an unconditional VMREAD if we add a comment stating that it's unnecessary if VM-Enter failed, but faster in the common case.