From 6b76896fb469f1a88bdab00a814b8cf9065c5bb9 Mon Sep 17 00:00:00 2001 From: Yosry Ahmed Date: Thu, 20 Nov 2025 13:06:55 -0500 Subject: [PATCH] KVM: SVM: Mark VMCB_LBR dirty when MSR_IA32_DEBUGCTLMSR is updated [ Upstream commit dc55b3c3f61246e483e50c85d8d5366f9567e188 ] The APM lists the DbgCtlMsr field as being tracked by the VMCB_LBR clean bit. Always clear the bit when MSR_IA32_DEBUGCTLMSR is updated. The history is complicated, it was correctly cleared for L1 before commit 1d5a1b5860ed ("KVM: x86: nSVM: correctly virtualize LBR msrs when L2 is running"). At that point svm_set_msr() started to rely on svm_update_lbrv() to clear the bit, but when nested virtualization is enabled the latter does not always clear it even if MSR_IA32_DEBUGCTLMSR changed. 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 Link: https://patch.msgid.link/20251108004524.1600006-2-yosry.ahmed@linux.dev Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini [ Open coded svm_get_lbr_vmcb() call ] Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- arch/x86/kvm/svm/svm.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index f56dcbbbf7341..00fb1c18e23a8 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -3053,11 +3053,17 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) if (data & DEBUGCTL_RESERVED_BITS) return 1; - if (svm->vmcb->control.virt_ext & LBR_CTL_ENABLE_MASK) + if (svm->vmcb->control.virt_ext & LBR_CTL_ENABLE_MASK) { + if (svm->vmcb->save.dbgctl == data) + break; svm->vmcb->save.dbgctl = data; - else + } else { + if (svm->vmcb01.ptr->save.dbgctl == data) + break; svm->vmcb01.ptr->save.dbgctl = data; + } + vmcb_mark_dirty(svm->vmcb, VMCB_LBR); svm_update_lbrv(vcpu); break; -- 2.47.3