[PATCH v4 2/5] KVM: x86: Prioritize CPUID faulting over CPUID VM-exits in nested VMX

[Jim Mattson <jmattson@google.com>]

Per the Intel SDM, "Certain exceptions have priority over VM exits.  These
include invalid-opcode exceptions, faults based on privilege level, and
general-protection exceptions that are based on checking I/O permission
bits in the task-state segment (TSS)."

Ensure that when L2 executes CPUID at CPL > 0 while L1 has enabled CPUID
faulting, KVM intercepts the exit in L0 and queues #GP rather than
forwarding the CPUID VM-exit to L1.

Empirical testing confirms that this #GP has higher precedence than a CPUID
VM-exit on Granite Rapids (F/M/S 6/0xad/1).

Fixes: db2336a80489 ("KVM: x86: virtualize cpuid faulting")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260513224608.1859737-1-jmattson%40google.com?part=3
Signed-off-by: Jim Mattson <jmattson@google.com>
---
 arch/x86/kvm/vmx/nested.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index a78ce0080963..30dcabc899a2 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -6552,6 +6552,8 @@ static bool nested_vmx_l0_wants_exit(struct kvm_vcpu *vcpu,
 			nested_evmcs_l2_tlb_flush_enabled(vcpu) &&
 			kvm_hv_is_tlb_flush_hcall(vcpu);
 #endif
+	case EXIT_REASON_CPUID:
+		return !kvm_is_cpuid_allowed(vcpu);
 	default:
 		break;
 	}
-- 
2.54.0.794.g4f17f83d09-goog