Inject a #GP if the guest attempts to change MSR_AMD64_DE_CFG from its
*current* value, not if the guest attempts to write a value other than
KVM's set of supported bits. As per the comment and the changelog of the
original code, the intent is to effectively make MSR_AMD64_DE_CFG read-
only for the guest.
Opportunistically use a more conventional equality check instead of an
exclusive-OR check to detect attempts to change bits.
Fixes: d1d93fa90f1a ("KVM: SVM: Add MSR-based feature support for serializing LFENCE")
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/svm/svm.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index c115d26844f7..550ead197543 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3189,8 +3189,13 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
if (data & ~msr_entry.data)
return 1;
- /* Don't allow the guest to change a bit, #GP */
- if (!msr->host_initiated && (data ^ msr_entry.data))
+ /*
+ * Don't let the guest change the host-programmed value. The
+ * MSR is very model specific, i.e. contains multiple bits that
+ * are completely unknown to KVM, and the one bit known to KVM
+ * is simply a reflection of hardware capatibilies.
+ */
+ if (!msr->host_initiated && data != svm->msr_decfg)
return 1;
svm->msr_decfg = data;
--
2.46.0.rc2.264.g509ed76dc8-goog
