This is a note to let you know that I've just added the patch titled
KVM: arm64: Avoid lock inversion when setting the VM register width
to the 6.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
kvm-arm64-avoid-lock-inversion-when-setting-the-vm-register-width.patch
and it can be found in the queue-6.2 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From c43120afb5c66a3465c7468f5cf9806a26484cde Mon Sep 17 00:00:00 2001
From: Oliver Upton <oliver.upton@xxxxxxxxx>
Date: Mon, 27 Mar 2023 16:47:45 +0000
Subject: KVM: arm64: Avoid lock inversion when setting the VM register width
From: Oliver Upton <oliver.upton@xxxxxxxxx>
commit c43120afb5c66a3465c7468f5cf9806a26484cde upstream.
kvm->lock must be taken outside of the vcpu->mutex. Of course, the
locking documentation for KVM makes this abundantly clear. Nonetheless,
the locking order in KVM/arm64 has been wrong for quite a while; we
acquire the kvm->lock while holding the vcpu->mutex all over the shop.
All was seemingly fine until commit 42a90008f890 ("KVM: Ensure lockdep
knows about kvm->lock vs. vcpu->mutex ordering rule") caught us with our
pants down, leading to lockdep barfing:
======================================================
WARNING: possible circular locking dependency detected
6.2.0-rc7+ #19 Not tainted
------------------------------------------------------
qemu-system-aar/859 is trying to acquire lock:
ffff5aa69269eba0 (&host_kvm->lock){+.+.}-{3:3}, at: kvm_reset_vcpu+0x34/0x274
but task is already holding lock:
ffff5aa68768c0b8 (&vcpu->mutex){+.+.}-{3:3}, at: kvm_vcpu_ioctl+0x8c/0xba0
which lock already depends on the new lock.
Add a dedicated lock to serialize writes to VM-scoped configuration from
the context of a vCPU. Protect the register width flags with the new
lock, thus avoiding the need to grab the kvm->lock while holding
vcpu->mutex in kvm_reset_vcpu().
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Jeremy Linton <jeremy.linton@xxxxxxx>
Link: https://lore.kernel.org/kvmarm/f6452cdd-65ff-34b8-bab0-5c06416da5f6@xxxxxxx/
Tested-by: Jeremy Linton <jeremy.linton@xxxxxxx>
Signed-off-by: Oliver Upton <oliver.upton@xxxxxxxxx>
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230327164747.2466958-3-oliver.upton@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm64/include/asm/kvm_host.h | 3 +++
arch/arm64/kvm/arm.c | 18 ++++++++++++++++++
arch/arm64/kvm/reset.c | 6 +++---
3 files changed, 24 insertions(+), 3 deletions(-)
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -191,6 +191,9 @@ struct kvm_arch {
/* Mandated version of PSCI */
u32 psci_version;
+ /* Protects VM-scoped configuration data */
+ struct mutex config_lock;
+
/*
* If we encounter a data abort without valid instruction syndrome
* information, report this to user space. User space can (and
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -138,6 +138,16 @@ int kvm_arch_init_vm(struct kvm *kvm, un
{
int ret;
+ mutex_init(&kvm->arch.config_lock);
+
+#ifdef CONFIG_LOCKDEP
+ /* Clue in lockdep that the config_lock must be taken inside kvm->lock */
+ mutex_lock(&kvm->lock);
+ mutex_lock(&kvm->arch.config_lock);
+ mutex_unlock(&kvm->arch.config_lock);
+ mutex_unlock(&kvm->lock);
+#endif
+
ret = kvm_share_hyp(kvm, kvm + 1);
if (ret)
return ret;
@@ -338,6 +348,14 @@ int kvm_arch_vcpu_create(struct kvm_vcpu
spin_lock_init(&vcpu->arch.mp_state_lock);
+#ifdef CONFIG_LOCKDEP
+ /* Inform lockdep that the config_lock is acquired after vcpu->mutex */
+ mutex_lock(&vcpu->mutex);
+ mutex_lock(&vcpu->kvm->arch.config_lock);
+ mutex_unlock(&vcpu->kvm->arch.config_lock);
+ mutex_unlock(&vcpu->mutex);
+#endif
+
/* Force users to call KVM_ARM_VCPU_INIT */
vcpu->arch.target = -1;
bitmap_zero(vcpu->arch.features, KVM_VCPU_MAX_FEATURES);
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -200,7 +200,7 @@ static int kvm_set_vm_width(struct kvm_v
is32bit = vcpu_has_feature(vcpu, KVM_ARM_VCPU_EL1_32BIT);
- lockdep_assert_held(&kvm->lock);
+ lockdep_assert_held(&kvm->arch.config_lock);
if (test_bit(KVM_ARCH_FLAG_REG_WIDTH_CONFIGURED, &kvm->arch.flags)) {
/*
@@ -253,9 +253,9 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu
bool loaded;
u32 pstate;
- mutex_lock(&vcpu->kvm->lock);
+ mutex_lock(&vcpu->kvm->arch.config_lock);
ret = kvm_set_vm_width(vcpu);
- mutex_unlock(&vcpu->kvm->lock);
+ mutex_unlock(&vcpu->kvm->arch.config_lock);
if (ret)
return ret;
Patches currently in stable-queue which might be from oliver.upton@xxxxxxxxx are
queue-6.2/kvm-arm64-use-config_lock-to-protect-vgic-state.patch
queue-6.2/kvm-arm64-vgic-don-t-acquire-its_lock-before-config_lock.patch
queue-6.2/kvm-arm64-use-config_lock-to-protect-data-ordered-against-kvm_run.patch
queue-6.2/kvm-arm64-avoid-vcpu-mutex-v.-kvm-lock-inversion-in-cpu_on.patch
queue-6.2/kvm-arm64-avoid-lock-inversion-when-setting-the-vm-register-width.patch
