From: sashiko-bot@kernel.org
To: "Sean Christopherson" <seanjc@google.com>
Cc: kvm@vger.kernel.org
Subject: Re: [PATCH v6 12/12] KVM: SVM: Add support for virtualizating Bus Lock Detect
Date: Wed, 30 Sep 2026 19:54:06 +0000 [thread overview]
Message-ID: <20260930195407.28A811F000FF@smtp.kernel.org> (raw)
In-Reply-To: <20260930193634.3415089-13-seanjc@google.com>
Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] kvm: svm: missing host_initiated check in MSR_IA32_DEBUGCTLMSR restoration
--
commit 6a801e9cb8e116e2aead8b9c8e78497f605d7a2c
Author: Ravi Bangoria <ravi.bangoria@amd.com>
KVM: SVM: Add support for virtualizating Bus Lock Detect
This commit advertises support for virtualizing Bus Lock Detect on SVM.
It allows the guest to enable BUS_LOCK_DETECT via MSR_IA32_DEBUGCTLMSR
if LBR Virtualization is enabled.
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index c3380d865b751..6d0242966dc87 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
[ ... ]
> @@ -789,7 +789,12 @@ BUILD_SVM_MSR_BITMAP_HELPERS(void, set, __set)
>
> static inline u64 svm_get_supported_debugctl(struct kvm_vcpu *vcpu)
> {
> - return DEBUGCTLMSR_LBR;
> + u64 debugctl = DEBUGCTLMSR_LBR;
> +
> + if (guest_cpu_cap_has(vcpu, X86_FEATURE_BUS_LOCK_DETECT))
> + debugctl |= DEBUGCTLMSR_BUS_LOCK_DETECT;
> +
[Severity: Medium]
Does this restrict host-initiated MSR restoration? By making the
DEBUGCTLMSR_BUS_LOCK_DETECT bit strictly dependent on guest_cpu_cap_has(),
this might reject host-initiated writes to MSR_IA32_DEBUGCTLMSR if the VMM
restores MSRs before initializing the guest CPUID.
In svm_set_msr(), the rejection happens unconditionally:
svm_set_msr()
if (data & ~svm_get_supported_debugctl(vcpu))
return 1;
Since svm_set_msr() does not appear to check msr->host_initiated before
enforcing this capability limit, could this regression break live
migration when userspace sends KVM_SET_MSRS before the CPUID is fully
configured?
> + return debugctl;
> }
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260930193634.3415089-1-seanjc@google.com?part=12
next prev parent reply other threads:[~2026-09-30 19:54 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-30 19:36 [PATCH v6 00/12] KVM: x86: Bus Lock Detect fixes and SVM support Sean Christopherson
2026-09-30 19:36 ` [PATCH v6 01/12] KVM: x86: Preserve DR6.BLD (Bus Lock Detect) when delivering #DB payload Sean Christopherson
2026-09-30 23:46 ` Shivansh Dhiman
2026-09-30 19:36 ` [PATCH v6 02/12] KVM: x86: Rename kvm_dr6_fixed() => kvm_get_dr6_fixed_1() Sean Christopherson
2026-09-30 19:36 ` [PATCH v6 03/12] KVM: Return an "unsigned long", not "u64" for the fixed-1 DR6 bits Sean Christopherson
2026-09-30 19:36 ` [PATCH v6 04/12] KVM: x86: Force fixed-1 bits in DR6 after synchronizing with hardware Sean Christopherson
2026-09-30 19:36 ` [PATCH v6 05/12] KVM: x86: Set guest's fixed-1 DR6 bits when delivering #DB payload Sean Christopherson
2026-09-30 19:36 ` [PATCH v6 06/12] KVM: x86: Kill off DR6_FIXED_1 to prevent future misuse Sean Christopherson
2026-09-30 19:36 ` [PATCH v6 07/12] KVM: SVM: Add helper to query if LBR virtualization needs to be enabled Sean Christopherson
2026-09-30 19:36 ` [PATCH v6 08/12] KVM: nSVM: Disable LBRV in nested control cache when unsupported Sean Christopherson
2026-09-30 19:36 ` [PATCH v6 09/12] KVM: nSVM: Open code check on LBR virtualization being enabled in vmcb12 Sean Christopherson
2026-09-30 19:36 ` [PATCH v6 10/12] KVM: nSVM: Don't assume all active-low bits DR6 are fixed-1 Sean Christopherson
2026-09-30 19:36 ` [PATCH v6 11/12] KVM: SVM: Add a vCPU-aware helper to get supported DEBUGCTL bits Sean Christopherson
2026-09-30 19:36 ` [PATCH v6 12/12] KVM: SVM: Add support for virtualizating Bus Lock Detect Sean Christopherson
2026-09-30 19:54 ` sashiko-bot [this message]
2026-09-30 20:20 ` Sean Christopherson
2026-10-02 21:07 ` [PATCH v6 00/12] KVM: x86: Bus Lock Detect fixes and SVM support Sean Christopherson
2026-10-05 5:46 ` Shivansh Dhiman
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