Re: [PATCH v2 15/15] KVM: x86/cpuid: Advertise Arch LBR feature in CPUID

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On 25/11/2022 12:06 pm, Yang Weijiang wrote:
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 85e3df6217af..60b3c591d462 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -134,6 +134,19 @@ static int kvm_check_cpuid(struct kvm_vcpu *vcpu,
  		if (vaddr_bits != 48 && vaddr_bits != 57 && vaddr_bits != 0)
  			return -EINVAL;
  	}
+	if (kvm_cpu_cap_has(X86_FEATURE_ARCH_LBR)) {
+		best = cpuid_entry2_find(entries, nent, 0x1c, 0);
+		if (best) {
+			unsigned int eax, ebx, ecx, edx;
+
+			/* Reject user-space CPUID if depth is different from host's.*/

Try to verify this in the KVM selftest, as this behavior is different from the host.

+			cpuid_count(0x1c, 0, &eax, &ebx, &ecx, &edx); > +
+			if ((eax & 0xff) &&
+			    (best->eax & 0xff) != BIT(fls(eax & 0xff) - 1))
+				return -EINVAL;
+		}
+	}



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