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AJvYcCWRS5T5GHqOfDIpolrIAhadQmbfGf5JhlL3PTeeK7sM3sPo/l7oJmAM8fp8d+mxt7CddjkqjxfSWbSC@lists.linux.dev X-Gm-Message-State: AOJu0YzIe+hsC2MNqFWs27CGTkxzbZsVd8QXSelqpy4cmwEvC5DTBKLE uKe/1pIp8ogZSOo0dqJK/aFBcZWAMsTBxOwLXN6f/xG/hHU7tL6QbVHi61bekW2vhfblVsHdyNe dL6+W3w== X-Received: from pjwo21.prod.google.com ([2002:a17:90a:d255:b0:356:213e:d56e]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:5710:b0:356:23be:7ecb with SMTP id 98e67ed59e1d1-35965c34bc7mr627146a91.12.1772149384979; Thu, 26 Feb 2026 15:43:04 -0800 (PST) Date: Thu, 26 Feb 2026 15:43:03 -0800 In-Reply-To: Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260214012702.2368778-1-seanjc@google.com> <20260214012702.2368778-8-seanjc@google.com> Message-ID: Subject: Re: [PATCH v3 07/16] KVM: SVM: Move core EFER.SVME enablement to kernel From: Sean Christopherson To: Chao Gao Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Kiryl Shutsemau , Peter Zijlstra , Arnaldo Carvalho de Melo , Namhyung Kim , Paolo Bonzini , linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev, kvm@vger.kernel.org, linux-perf-users@vger.kernel.org, Xu Yilun , Dan Williams Content-Type: text/plain; charset="us-ascii" On Thu, Feb 26, 2026, Chao Gao wrote: > >-static inline void kvm_cpu_svm_disable(void) > >-{ > >- uint64_t efer; > >- > >- wrmsrq(MSR_VM_HSAVE_PA, 0); > >- rdmsrq(MSR_EFER, efer); > >- if (efer & EFER_SVME) { > >- /* > >- * Force GIF=1 prior to disabling SVM, e.g. to ensure INIT and > >- * NMI aren't blocked. > >- */ > >- stgi(); > >- wrmsrq(MSR_EFER, efer & ~EFER_SVME); > >- } > >-} > >- > > static void svm_emergency_disable_virtualization_cpu(void) > > { > >- virt_rebooting = true; > >- > >- kvm_cpu_svm_disable(); > >+ wrmsrq(MSR_VM_HSAVE_PA, 0); > > } > > > > static void svm_disable_virtualization_cpu(void) > >@@ -507,7 +489,7 @@ static void svm_disable_virtualization_cpu(void) > > if (tsc_scaling) > > __svm_write_tsc_multiplier(SVM_TSC_RATIO_DEFAULT); > > > >- kvm_cpu_svm_disable(); > >+ x86_svm_disable_virtualization_cpu(); > > There's a functional change here. The new x86_svm_disable_virtualization_cpu() > doesn't reset MSR_VM_HSAVE_PA, but the old kvm_cpu_svm_disable() does. Doh. I'll squash this as fixup, assuming there are no other goofs: diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 5f033bf3ba83..fc08450cb4b7 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -490,6 +490,7 @@ static void svm_disable_virtualization_cpu(void) __svm_write_tsc_multiplier(SVM_TSC_RATIO_DEFAULT); x86_svm_disable_virtualization_cpu(); + wrmsrq(MSR_VM_HSAVE_PA, 0); amd_pmu_disable_virt(); } Very nice catch! P.S. This reminded me that there's a lurking wart with __sev_snp_init_locked() where it forces MSR_VM_HSAVE_PA to '0' on all CPUs. That's firmly a "hypervisor" thing so it doesn't really fit here (and code wise it's also kludgy), just thought I'd mention it in case someone has a brilliant idea and/or runs into problems with it. IIRC, we ran into a problem where __sev_snp_init_locked() clobbered KVM's value, but I think the underlying problem was effectively fixed by commit 6f1d5a3513c2 ("KVM: SVM: Add support to initialize SEV/SNP functionality in KVM").