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Peter Anvin" , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Jamie Liu Content-Type: text/plain; charset="us-ascii" On Tue, Feb 10, 2026, Jim Mattson wrote: > The Intel Virtualization Technology FlexMigration Application Note says, > "When CPUID faulting is enabled, all executions of the CPUID instruction > outside system-management mode (SMM) cause a general-protection exception > (#GP(0)) if the current privilege level (CPL) is greater than 0." > > Always allow the execution of CPUID in SMM. > > Fixes: db2336a80489 ("KVM: x86: virtualize cpuid faulting") I feel like we need a Technically-fixes-but-really-just-a-bad-spec tag for things like this. MISC_ENABLES and MSR_K7_HWCR in particular are a bizarre game of "Hold my beer!". > Signed-off-by: Jim Mattson > --- > arch/x86/kvm/cpuid.c | 3 ++- > arch/x86/kvm/emulate.c | 6 +++--- > 2 files changed, 5 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > index 7fe4e58a6ebf..863ce81023e9 100644 > --- a/arch/x86/kvm/cpuid.c > +++ b/arch/x86/kvm/cpuid.c > @@ -2157,7 +2157,8 @@ int kvm_emulate_cpuid(struct kvm_vcpu *vcpu) > { > u32 eax, ebx, ecx, edx; > > - if (cpuid_fault_enabled(vcpu) && !kvm_require_cpl(vcpu, 0)) > + if (!is_smm(vcpu) && cpuid_fault_enabled(vcpu) && > + !kvm_require_cpl(vcpu, 0)) > return 1; > > eax = kvm_rax_read(vcpu); > diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c > index c8e292e9a24d..4b7289a82bf8 100644 > --- a/arch/x86/kvm/emulate.c > +++ b/arch/x86/kvm/emulate.c > @@ -3583,10 +3583,10 @@ static int em_cpuid(struct x86_emulate_ctxt *ctxt) > u64 msr = 0; > > ctxt->ops->get_msr(ctxt, MSR_MISC_FEATURES_ENABLES, &msr); > - if (msr & MSR_MISC_FEATURES_ENABLES_CPUID_FAULT && > - ctxt->ops->cpl(ctxt)) { > + if (!ctxt->ops->is_smm(ctxt) && > + (msr & MSR_MISC_FEATURES_ENABLES_CPUID_FAULT && > + ctxt->ops->cpl(ctxt))) I assume you intended the parentheses to wrap the bitwise-AND. I'll fixup to this when applying. if (!ctxt->ops->is_smm(ctxt) && (msr & MSR_MISC_FEATURES_ENABLES_CPUID_FAULT) && ctxt->ops->cpl(ctxt))