Clear the VMCB_LBR clean bit when MSR_IA32_DEBUGCTLMSR is updated, as the only valid bit is DEBUGCTLMSR_LBR. The history is complicated, it was correctly cleared for L1 before commit 1d5a1b5860ed ("KVM: x86: nSVM: correctly virtualize LBR msrs when L2 is running"), then the latter relied on svm_update_lbrv() to clear it, but it only did so for L2. Go back to clearing it directly in svm_set_msr(). Fixes: 1d5a1b5860ed ("KVM: x86: nSVM: correctly virtualize LBR msrs when L2 is running") Reported-by: Matteo Rizzo Reported-by: evn@google.com Co-developed-by: Jim Mattson Signed-off-by: Jim Mattson Signed-off-by: Yosry Ahmed --- arch/x86/kvm/svm/svm.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 55bd7aa5cd743..d25c56b30b4e2 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -3009,7 +3009,11 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) if (data & DEBUGCTL_RESERVED_BITS) return 1; + if (svm_get_lbr_vmcb(svm)->save.dbgctl == data) + break; + svm_get_lbr_vmcb(svm)->save.dbgctl = data; + vmcb_mark_dirty(svm->vmcb, VMCB_LBR); svm_update_lbrv(vcpu); break; case MSR_VM_HSAVE_PA: -- 2.51.2.1041.gc1ab5b90ca-goog