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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id s23sm3820305wmc.29.2021.02.17.08.29.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 17 Feb 2021 08:29:27 -0800 (PST) Subject: Re: [PATCH 1/7] KVM: VMX: read idt_vectoring_info a bit earlier To: Sean Christopherson , Maxim Levitsky Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Wanpeng Li , Borislav Petkov , Joerg Roedel , Jim Mattson , "H. Peter Anvin" , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , Thomas Gleixner , Vitaly Kuznetsov , Ingo Molnar References: <20210217145718.1217358-1-mlevitsk@redhat.com> <20210217145718.1217358-2-mlevitsk@redhat.com> <09de977a-0275-0f4f-cf75-f45e4b5d9ca5@redhat.com> <666eb754189a380899b82e0a9798eb2560ae6972.camel@redhat.com> From: Paolo Bonzini Message-ID: <26f7ee7b-568f-c838-d0e0-db125cfbd4e5@redhat.com> Date: Wed, 17 Feb 2021 17:29:26 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17/02/21 17:21, Sean Christopherson wrote: > 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. It's okay, just good to know! Thanks, paolo