FAILED: patch "[PATCH] KVM: arm64: nv: Delay freeing of shadow S2 structures until" failed to apply to 6.12-stable tree

PATCH New [email protected] 2 participants 3 messages Sep 29 – Sep 30

Subsystems (3)

Stable branch arm64 KVM arm64

lore

Share & tools

lore

[email protected]

author maintainer

2026-09-29 11:39 UTC #0 lore raw

The patch below does not apply to the 6.12-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 <[email protected]>.

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-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x e5843f4effaa2ffac3e789ecd4456403564961d4
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026092945-plastic-corrosive-d2d1@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From e5843f4effaa2ffac3e789ecd4456403564961d4 Mon Sep 17 00:00:00 2001
From: Marc Zyngier <[email protected]>
Date: Fri, 11 Sep 2026 17:22:03 +0100
Subject: [PATCH] KVM: arm64: nv: Delay freeing of shadow S2 structures until
VM destruction

We free the shadow S2 structures from kvm_arch_flush_shadow_all(), which is a Bad Idea(tm). Freeing the page tables is fair game (this is what this callback is for), but freeing the container that could still be referenced by another part of the system is not great.

Instead, grow separate destructors that gets called when we tear the VM down for good. From there, we can nuke both the individual MMUs as well as the global array that points to them, safe in the knowledge that the vcpus themselves have been destroyed already.

Fixes 4f128f8e1aaac ("KVM: arm64: nv: Support multiple nested Stage-2 mmu structures")

Reviewed-by Lorenzo Stoakes (ARM) <[email protected]>

Signed-off-by Marc Zyngier <[email protected]>

Cc [email protected]

Reviewed-by Wei-Lin Chang <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Oliver Upton <[email protected]>

arch/arm64/include/asm/kvm_nested.h +1 -0

index 5b8edb2e8a87..586026e85903 100644
@@ -67,6 +67,7 @@ static inline u64 translate_ttbr0_el2_to_ttbr0_el1(u64 ttbr0)
 extern bool forward_smc_trap(struct kvm_vcpu *vcpu);
 extern bool forward_debug_exception(struct kvm_vcpu *vcpu);
 extern int kvm_init_nested(struct kvm *kvm);
+extern void kvm_destroy_nested(struct kvm *kvm);
 extern int kvm_vcpu_init_nested(struct kvm_vcpu *vcpu);
 extern void kvm_init_nested_s2_mmu(struct kvm_s2_mmu *mmu);
 extern struct kvm_s2_mmu *lookup_s2_mmu(struct kvm_vcpu *vcpu);

arch/arm64/kvm/arm.c +2 -2

index b53219e048bd..eaf583b77193 100644
@@ -282,7 +282,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 
 err_uninit_mmu:
 	kvm_uninit_stage2_mmu(kvm);
-	kvfree(kvm->arch.nested_mmus);
+	kvm_destroy_nested(kvm);
 err_free_cpumask:
 	free_cpumask_var(kvm->arch.supported_cpus);
 err_unshare_kvm:

@@ -340,7 +340,7 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
 
 	kvm_unshare_hyp(kvm, kvm + 1);
 
-	kvfree(kvm->arch.nested_mmus);
+	kvm_destroy_nested(kvm);
 	kvm_arm_teardown_hypercalls(kvm);
 }

arch/arm64/kvm/nested.c +10 -5

index 2571f177e654..b191365d97cc 100644
@@ -56,6 +56,15 @@ int kvm_init_nested(struct kvm *kvm)
 	return kvm->arch.nested_mmus ? 0 : -ENOMEM;
 }
 
+void kvm_destroy_nested(struct kvm *kvm)
+{
+	for (int i = 0; i < kvm->arch.nested_mmus_size; i+= S2_MMU_PER_VCPU)
+		kvfree(kvm->arch.nested_mmus[i]);
+
+	kvm->arch.nested_mmus_size = 0;
+	kvfree(kvm->arch.nested_mmus);
+}
+
 static int init_nested_s2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu)
 {
 	/*

@@ -1322,16 +1331,12 @@ void kvm_nested_s2_flush(struct kvm *kvm)
 
 void kvm_arch_flush_shadow_all(struct kvm *kvm)
 {
-	for (int i = kvm->arch.nested_mmus_size - 1; i >= 0; i--) {
+	for (int i = 0; i < kvm->arch.nested_mmus_size; i++) {
 		struct kvm_s2_mmu *mmu = kvm->arch.nested_mmus[i];
 
 		if (!WARN_ON(atomic_read(&mmu->refcnt)))
 			kvm_free_stage2_pgd(mmu);
-
-		if ((i % S2_MMU_PER_VCPU) == 0)
-			kvfree(mmu);
 	}
-	kvm->arch.nested_mmus_size = 0;
 	kvm_uninit_stage2_mmu(kvm);
 }

Sasha Levin

maintainer

2026-09-30 15:09 UTC #1 lore raw

PATCH 1/2 KVM: arm64: nv: Fix life cycle of the nested_mmus array

From: Marc Zyngier <[email protected]>

[ Upstream commit 33346f8960c7bb6a3b4e273b5cfe25c5a8be349f ]

The nested_mmus array holds the shadow page tables that are used when a guest is running a nested context. These structures are allocated on VCPU_INIT for whole guest, which implies that they may have to be relocated as the array grows.

Should a VCPU_INIT occur whilst a vcpu is actively running an L2 and that the allocation requires relocation, that vcpu will still be running with a pointer to the previous structure, which will have been freed.

Fix this by turning the array of structures to an array of pointers, which is now allocated at VM creation, sized to the absolute maximum that KVM can handle.

In turn, each VCPU_INIT contributes S2_MMU_PER_VCPU to the pool. No reallocation is ever performed, and the life cycle of each object is much clearer:

- the nested_mmus array is allocated in kvm_init_nested(), and freed in kvm_arch_destroy_vm()

- s2_mmu structures are allocated in kvm_vcpu_init_nested(), and freed on kvm_arch_flush_shadow_all()

Finally, the freeing of vcpu->arch.vncr_array is made consistent rather than being done on some failure paths, but not others.

Fixes 4f128f8e1aaa ("KVM: arm64: nv: Support multiple nested Stage-2 mmu structures")

Reported-by Shen Yongchao <[email protected]>

Reported-by Karl Mehltretter <[email protected]>

Acked-by Lorenzo Stoakes (ARM) <[email protected]>

Link https://lore.kernel.org/r/[email protected] open here

Signed-off-by Marc Zyngier <[email protected]>

Cc [email protected]

Reviewed-by Wei-Lin Chang <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Oliver Upton <[email protected]>

[6.12 backport: Retain the fixed pointer array and per-vCPU MMU batches, including publication under mmu_lock and cleanup of partially initialized batches. Add the stage-2 unwind label to the existing VM initialization path without importing the newer protected-VM setup. Omit VNCR allocation, VNCR TLB accounting, E2H0 checks and the debug-exception declaration, whose support is absent here. No new functions are introduced. Keep the MMU cleanup layout needed by e5843f4effaa ("KVM: arm64: nv: Delay freeing of shadow S2 structures until VM destruction").]

Stable-dep-of: e5843f4effaa ("KVM: arm64: nv: Delay freeing of shadow S2 structures until VM destruction")

Signed-off-by Sasha Levin <[email protected]>

---
 arch/arm64/include/asm/kvm_host.h   |  2 +-
 arch/arm64/include/asm/kvm_nested.h |  2 +-
 arch/arm64/kvm/arm.c                | 10 +++-
 arch/arm64/kvm/nested.c             | 88 +++++++++++++++--------------
 4 files changed, 55 insertions(+), 47 deletions(-)

arch/arm64/include/asm/kvm_host.h +1 -1

index ab0402642f347..4f6afd2c042fe 100644
@@ -292,7 +292,7 @@ struct kvm_arch {
 	 * Stage 2 paging state for VMs with nested S2 using a virtual
 	 * VMID.
 	 */
-	struct kvm_s2_mmu *nested_mmus;
+	struct kvm_s2_mmu **nested_mmus;
 	size_t nested_mmus_size;
 	int nested_mmus_next;

arch/arm64/include/asm/kvm_nested.h +1 -1

index 233e655227164..d9250fa8cdd03 100644
@@ -64,7 +64,7 @@ static inline u64 translate_ttbr0_el2_to_ttbr0_el1(u64 ttbr0)
 }
 
 extern bool forward_smc_trap(struct kvm_vcpu *vcpu);
-extern void kvm_init_nested(struct kvm *kvm);
+extern int kvm_init_nested(struct kvm *kvm);
 extern int kvm_vcpu_init_nested(struct kvm_vcpu *vcpu);
 extern void kvm_init_nested_s2_mmu(struct kvm_s2_mmu *mmu);
 extern struct kvm_s2_mmu *lookup_s2_mmu(struct kvm_vcpu *vcpu);

arch/arm64/kvm/arm.c +8 -2

index 72e4c290d8fca..ec229e6a0b731 100644
@@ -181,8 +181,6 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 	mutex_unlock(&kvm->lock);
 #endif
 
-	kvm_init_nested(kvm);
-
 	ret = kvm_share_hyp(kvm, kvm + 1);
 	if (ret)
 		return ret;

@@ -201,6 +199,10 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 	if (ret)
 		goto err_free_cpumask;
 
+	ret = kvm_init_nested(kvm);
+	if (ret)
+		goto err_uninit_mmu;
+
 	kvm_vgic_early_init(kvm);
 
 	kvm_timer_init_vm(kvm);

@@ -214,6 +216,9 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 
 	return 0;
 
+err_uninit_mmu:
+	kvm_uninit_stage2_mmu(kvm);
+	kvfree(kvm->arch.nested_mmus);
 err_free_cpumask:
 	free_cpumask_var(kvm->arch.supported_cpus);
 err_unshare_kvm:

@@ -270,6 +275,7 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
 
 	kvm_unshare_hyp(kvm, kvm + 1);
 
+	kvfree(kvm->arch.nested_mmus);
 	kvm_arm_teardown_hypercalls(kvm);
 }

arch/arm64/kvm/nested.c +45 ~~-43~~

155 lines not on this page · raw message

Signature · 1 line

2.53.0

Sasha Levin

maintainer

2026-09-30 15:09 UTC #2 lore raw

PATCH 2/2 KVM: arm64: nv: Delay freeing of shadow S2 structures until VM destruction

From: Marc Zyngier <[email protected]>

[ Upstream commit e5843f4effaa2ffac3e789ecd4456403564961d4 ]

Fixes 4f128f8e1aaac ("KVM: arm64: nv: Support multiple nested Stage-2 mmu structures")

Reviewed-by Lorenzo Stoakes (ARM) <[email protected]>

Signed-off-by Marc Zyngier <[email protected]>

Cc [email protected]

Reviewed-by Wei-Lin Chang <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Oliver Upton <[email protected]>

Signed-off-by Sasha Levin <[email protected]>

---
 arch/arm64/include/asm/kvm_nested.h |  1 +
 arch/arm64/kvm/arm.c                |  4 ++--
 arch/arm64/kvm/nested.c             | 15 ++++++++++-----
 3 files changed, 13 insertions(+), 7 deletions(-)

arch/arm64/include/asm/kvm_nested.h +1 -0

index d9250fa8cdd03..ae3a285e99d06 100644
@@ -65,6 +65,7 @@ static inline u64 translate_ttbr0_el2_to_ttbr0_el1(u64 ttbr0)
 
 extern bool forward_smc_trap(struct kvm_vcpu *vcpu);
 extern int kvm_init_nested(struct kvm *kvm);
+extern void kvm_destroy_nested(struct kvm *kvm);
 extern int kvm_vcpu_init_nested(struct kvm_vcpu *vcpu);
 extern void kvm_init_nested_s2_mmu(struct kvm_s2_mmu *mmu);
 extern struct kvm_s2_mmu *lookup_s2_mmu(struct kvm_vcpu *vcpu);

arch/arm64/kvm/arm.c +2 -2

index ec229e6a0b731..2a156ddf0c314 100644
@@ -218,7 +218,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 
 err_uninit_mmu:
 	kvm_uninit_stage2_mmu(kvm);
-	kvfree(kvm->arch.nested_mmus);
+	kvm_destroy_nested(kvm);
 err_free_cpumask:
 	free_cpumask_var(kvm->arch.supported_cpus);
 err_unshare_kvm:

@@ -275,7 +275,7 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
 
 	kvm_unshare_hyp(kvm, kvm + 1);
 
-	kvfree(kvm->arch.nested_mmus);
+	kvm_destroy_nested(kvm);
 	kvm_arm_teardown_hypercalls(kvm);
 }

arch/arm64/kvm/nested.c +10 -5

index aae70f62133a6..45836a9c001d1 100644
@@ -37,6 +37,15 @@ int kvm_init_nested(struct kvm *kvm)
 	return kvm->arch.nested_mmus ? 0 : -ENOMEM;
 }
 
+void kvm_destroy_nested(struct kvm *kvm)
+{
+	for (int i = 0; i < kvm->arch.nested_mmus_size; i+= S2_MMU_PER_VCPU)
+		kvfree(kvm->arch.nested_mmus[i]);
+
+	kvm->arch.nested_mmus_size = 0;
+	kvfree(kvm->arch.nested_mmus);
+}
+
 static int init_nested_s2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu)
 {
 	/*

@@ -788,16 +797,12 @@ void kvm_nested_s2_flush(struct kvm *kvm)
 
 void kvm_arch_flush_shadow_all(struct kvm *kvm)
 {
-	for (int i = kvm->arch.nested_mmus_size - 1; i >= 0; i--) {
+	for (int i = 0; i < kvm->arch.nested_mmus_size; i++) {
 		struct kvm_s2_mmu *mmu = kvm->arch.nested_mmus[i];
 
 		if (!WARN_ON(atomic_read(&mmu->refcnt)))
 			kvm_free_stage2_pgd(mmu);
-
-		if ((i % S2_MMU_PER_VCPU) == 0)
-			kvfree(mmu);
 	}
-	kvm->arch.nested_mmus_size = 0;
 	kvm_uninit_stage2_mmu(kvm);
 }

Signature · 1 line

2.53.0