From: Sean Christopherson <seanjc@google.com>
Date: Tue, 13 Jul 2021 09:32:43 -0700
Subject: KVM: SVM: Require exact CPUID.0x1 match when stuffing EDX at INIT
Git-commit: 067a456d091d05fdae32cae350410d905968b645
Patch-mainline: v5.15-rc1
References: bsc#1194650

Do not allow an inexact CPUID "match" when querying the guest's CPUID.0x1
to stuff EDX during INIT.  In the common case, where the guest CPU model
is an AMD variant, allowing an inexact match is a nop since KVM doesn't
emulate Intel's goofy "out-of-range" logic for AMD and Hygon.  If the
vCPU model happens to be an Intel variant, an inexact match is possible
if and only if the max CPUID leaf is precisely '0'. Aside from the fact
that there's probably no CPU in existence with a single CPUID leaf, if
the max CPUID leaf is '0', that means that CPUID.0.EAX is '0', and thus
an inexact match for CPUID.0x1.EAX will also yield '0'.

So, with lots of twisty logic, no functional change intended.

Reviewed-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-6-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Dario Faggioli <dfaggioli@suse.com>
---
 arch/x86/kvm/svm/svm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 7845232b6fb6..f4b6fec6252f 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1346,7 +1346,7 @@ static void svm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 	}
 	init_vmcb(vcpu);
 
-	kvm_cpuid(vcpu, &eax, &dummy, &dummy, &dummy, false);
+	kvm_cpuid(vcpu, &eax, &dummy, &dummy, &dummy, true);
 	kvm_rdx_write(vcpu, eax);
 
 	if (kvm_vcpu_apicv_active(vcpu) && !init_event)