[PATCH 6.18.y v2 1/6] KVM: x86: Ignore cpuid faulting in SMM

[Anil Altinay <aaltinay@google.com>]

From: Jim Mattson <jmattson@google.com>

commit 690dc03859e7907bc995f389618c748619559477 upstream.

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")
Signed-off-by: Jim Mattson <jmattson@google.com>
Link: https://patch.msgid.link/20260210234613.1383279-1-jmattson@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Anil Altinay <aaltinay@google.com>
---
 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 913ffb995279..bfa89fbe826b 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -2098,7 +2098,8 @@ 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 9dbf3623e79e..8aa10d0e9894 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3560,10 +3560,10 @@ 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))
 		return emulate_gp(ctxt, 0);
-	}
 
 	eax = reg_read(ctxt, VCPU_REGS_RAX);
 	ecx = reg_read(ctxt, VCPU_REGS_RCX);
-- 
2.56.0.385.gd3acb90ef8-goog