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KVM: VMX: Allow guest to set DEBUGCTL.RTM_DEBUG if RTM is supported

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Let the guest set DEBUGCTL.RTM_DEBUG if RTM is supported according to the
guest CPUID model, as debug support is supposed to be available if RTM is
supported, and there are no known downsides to letting the guest debug RTM
aborts.

Note, there are no known bug reports related to RTM_DEBUG, the primary
motivation is to reduce the probability of breaking existing guests when a
future change adds a missing consistency check on vmcs12.GUEST_DEBUGCTL
(KVM currently lets L2 run with whatever hardware supports; whoops).

Note #2, KVM already emulates DR6.RTM, and doesn't restrict access to
DR7.RTM.

Fixes: 83c529151a ("KVM: x86: expose Intel cpu new features (HLE, RTM) to guest")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20250610232010.162191-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2025-06-10 16:20:06 -07:00
parent 80c64c7afe
commit 17ec2f9653
2 changed files with 5 additions and 0 deletions
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1
arch/x86/include/asm/msr-index.h
View File

@ -419,6 +419,7 @@
#define DEBUGCTLMSR_FREEZE_PERFMON_ON_PMI (1UL << 12)
#define DEBUGCTLMSR_FREEZE_IN_SMM_BIT 14
#define DEBUGCTLMSR_FREEZE_IN_SMM (1UL << DEBUGCTLMSR_FREEZE_IN_SMM_BIT)
#define DEBUGCTLMSR_RTM_DEBUG BIT(15)
#define MSR_PEBS_FRONTEND 0x000003f7

4
arch/x86/kvm/vmx/vmx.c
View File

@ -2186,6 +2186,10 @@ static u64 vmx_get_supported_debugctl(struct kvm_vcpu *vcpu, bool host_initiated
(host_initiated || intel_pmu_lbr_is_enabled(vcpu)))
debugctl |= DEBUGCTLMSR_LBR | DEBUGCTLMSR_FREEZE_LBRS_ON_PMI;
if (boot_cpu_has(X86_FEATURE_RTM) &&
(host_initiated || guest_cpu_cap_has(vcpu, X86_FEATURE_RTM)))
debugctl |= DEBUGCTLMSR_RTM_DEBUG;
return debugctl;
}