FAILED: patch "[PATCH] KVM: SVM: Mark VMCB_LBR dirty when MSR_IA32_DEBUGCTLMSR is" failed to apply to 6.1-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x dc55b3c3f61246e483e50c85d8d5366f9567e188
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025112036-abdominal-envelope-7ca0@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From dc55b3c3f61246e483e50c85d8d5366f9567e188 Mon Sep 17 00:00:00 2001
From: Yosry Ahmed <yosry.ahmed@linux.dev>
Date: Sat, 8 Nov 2025 00:45:19 +0000
Subject: [PATCH] KVM: SVM: Mark VMCB_LBR dirty when MSR_IA32_DEBUGCTLMSR is
 updated

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 <matteorizzo@google.com>
Reported-by: evn@google.com
Co-developed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Link: https://patch.msgid.link/20251108004524.1600006-2-yosry.ahmed@linux.dev
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 76055c0ba177..39538098002b 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3004,7 +3004,11 @@ 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: