FAILED: patch "[PATCH] KVM: arm64: vgic: Stop the target vcpu when disabling LPIs" failed to apply to 6.18-stable tree

FAILED: patch "[PATCH] KVM: arm64: vgic: Stop the target vcpu when disabling LPIs" failed to apply to 6.18-stable tree

[Sasha Levin]

The patch below does not apply to the 6.18-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-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x a1b4bd2c2c262b8094c86afb99364d16ac08cb66
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107051145-failed-6.18-a1b4bd2c2c26@kernel.org' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Thanks,
Sasha

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

From a1b4bd2c2c262b8094c86afb99364d16ac08cb66 Mon Sep 17 00:00:00 2001
From: Marc Zyngier <maz@kernel.org>
Date: Thu, 15 Oct 2026 11:05:38 +0100
Subject: [PATCH] KVM: arm64: vgic: Stop the target vcpu when disabling LPIs

Disabling LPIs is pretty nasty, as it directly messes with the AP list
of the affected CPU, which could be running... This has the potential to
lead to really bad behaviours, and we should not be doing that.

Take example on the way the Active state is handled and simply pause the
the vcpu so that we are sure it is in a quiescent state, and the state be
safely manipulated.

Nobody has any expectation of performance for this anyway.

Fixes: 96085b949672d ("KVM: arm/arm64: vgic-v3: Retire pending interrupts on disabling LPIs")
Co-developed-by: Oliver Upton <oupton@kernel.org>
Signed-off-by: Oliver Upton <oupton@kernel.org>
Cc: stable@vger.kernel.org
Reviewed-by: Fuad Tabba <fuad.tabba@linux.dev>
Tested-by: Fuad Tabba <fuad.tabba@linux.dev>
Link: https://patch.msgid.link/20261015100539.1011760-7-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/kvm/vgic/vgic-mmio-v3.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/arm64/kvm/vgic/vgic-mmio-v3.c b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
index 5913a20d83019..f5bd29fbe3a90 100644
--- a/arch/arm64/kvm/vgic/vgic-mmio-v3.c
+++ b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
@@ -303,9 +303,19 @@ static void vgic_mmio_write_v3r_ctlr(struct kvm_vcpu *vcpu,
 		if (ctlr != GICR_CTLR_ENABLE_LPIS)
 			return;
 
+		/*
+		 * Yes, disabling LPIs is painful, since it can be done from
+		 * a *remote* vcpu! So let's not take any chance, and make
+		 * sure that the target vCPU has written their LRs back to the
+		 * irq structures, and release any reference they would have.
+		 *
+		 * If it hurts, don't do it.
+		 */
+		kvm_pause_vcpu(vcpu);
 		vgic_flush_pending_lpis(vcpu);
 		vgic_its_invalidate_all_caches(vcpu->kvm);
 		atomic_set_release(&vgic_cpu->ctlr, 0);
+		kvm_resume_vcpu(vcpu);
 	} else {
 		ctlr = atomic_cmpxchg_acquire(&vgic_cpu->ctlr, 0,
 					      GICR_CTLR_ENABLE_LPIS);
-- 
2.53.0

[PATCH 6.18.y] KVM: arm64: vgic: Stop the target vcpu when disabling LPIs

[Sasha Levin]

From: Marc Zyngier <maz@kernel.org>

[ Upstream commit a1b4bd2c2c262b8094c86afb99364d16ac08cb66 ]

Disabling LPIs is pretty nasty, as it directly messes with the AP list
of the affected CPU, which could be running... This has the potential to
lead to really bad behaviours, and we should not be doing that.

Take example on the way the Active state is handled and simply pause the
the vcpu so that we are sure it is in a quiescent state, and the state be
safely manipulated.

Nobody has any expectation of performance for this anyway.

Fixes: 96085b949672d ("KVM: arm/arm64: vgic-v3: Retire pending interrupts on disabling LPIs")
Co-developed-by: Oliver Upton <oupton@kernel.org>
Signed-off-by: Oliver Upton <oupton@kernel.org>
Cc: stable@vger.kernel.org
Reviewed-by: Fuad Tabba <fuad.tabba@linux.dev>
Tested-by: Fuad Tabba <fuad.tabba@linux.dev>
Link: https://patch.msgid.link/20261015100539.1011760-7-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
[ sashal: Replaced missing kvm_pause_vcpu() and kvm_resume_vcpu() calls with whole-guest kvm_arm_halt_guest() and kvm_arm_resume_guest() calls. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/arm64/kvm/vgic/vgic-mmio-v3.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/arm64/kvm/vgic/vgic-mmio-v3.c b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
index 79e018cec0f96..5ba3bb576bb15 100644
--- a/arch/arm64/kvm/vgic/vgic-mmio-v3.c
+++ b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
@@ -303,9 +303,19 @@ static void vgic_mmio_write_v3r_ctlr(struct kvm_vcpu *vcpu,
 		if (ctlr != GICR_CTLR_ENABLE_LPIS)
 			return;
 
+		/*
+		 * Yes, disabling LPIs is painful, since it can be done from
+		 * a *remote* vcpu! So let's not take any chance, and make
+		 * sure that the target vCPU has written their LRs back to the
+		 * irq structures, and release any reference they would have.
+		 *
+		 * If it hurts, don't do it.
+		 */
+		kvm_arm_halt_guest(vcpu->kvm);
 		vgic_flush_pending_lpis(vcpu);
 		vgic_its_invalidate_all_caches(vcpu->kvm);
 		atomic_set_release(&vgic_cpu->ctlr, 0);
+		kvm_arm_resume_guest(vcpu->kvm);
 	} else {
 		ctlr = atomic_cmpxchg_acquire(&vgic_cpu->ctlr, 0,
 					      GICR_CTLR_ENABLE_LPIS);
-- 
2.53.0