Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 20 Oct 2021 18:38:06 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     Tom Lendacky <thomas.lendacky@amd.com>
Cc:     Joerg Roedel <joro@8bytes.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>, x86@kernel.org,
        Brijesh Singh <brijesh.singh@amd.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, Joerg Roedel <jroedel@suse.de>
Subject: Re: [PATCH v5 4/6] KVM: SVM: Add support to handle AP reset MSR
 protocol
Message-ID: <YXBiDr5mgtkgwBDR@google.com>
References: <20211020124416.24523-1-joro@8bytes.org>
 <20211020124416.24523-5-joro@8bytes.org>
 <YXBUlYll8JDjH/Wd@google.com>
 <95d99b9a-8600-619b-9b83-63597d937bc6@amd.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <95d99b9a-8600-619b-9b83-63597d937bc6@amd.com>
Precedence: bulk

On Wed, Oct 20, 2021, Tom Lendacky wrote:
> On 10/20/21 12:40 PM, Sean Christopherson wrote:
> > On Wed, Oct 20, 2021, Joerg Roedel wrote:
> > This can race with the SIPI and effectively corrupt svm->vmcb->control.ghcb_gpa.
> > 
> >          vCPU0                           vCPU1
> >                                          #VMGEXIT(RESET_HOLD)
> >                                          __kvm_vcpu_halt()
> >          INIT
> >          SIPI
> >          sev_vcpu_deliver_sipi_vector()
> >          ghcb_msr_ap_rst_resp(1);
> 
> This isn't possible. vCPU0 doesn't set vCPU1's GHCB value. vCPU1's GHCB
> value is set when vCPU1 handles events in vcpu_enter_guest().

Argh, I was thinking of injecting regular IPIs across vCPUs.  In hindsight it
makes sense that INIT and SIPI are handled on the current vCPU, stuffing all that
state from a different vCPU would be needlessly complex.