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KVM: arm64: use kvm_trylock_all_vcpus when locking all vCPUs
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Use kvm_trylock_all_vcpus instead of a custom implementation when locking
all vCPUs of a VM, to avoid triggering a lockdep warning, in the case in
which the VM is configured to have more than MAX_LOCK_DEPTH vCPUs.

This fixes the following false lockdep warning:

[  328.171264] BUG: MAX_LOCK_DEPTH too low!
[  328.175227] turning off the locking correctness validator.
[  328.180726] Please attach the output of /proc/lock_stat to the bug report
[  328.187531] depth: 48  max: 48!
[  328.190678] 48 locks held by qemu-kvm/11664:
[  328.194957]  #0: ffff800086de5ba0 (&kvm->lock){+.+.}-{3:3}, at: kvm_ioctl_create_device+0x174/0x5b0
[  328.204048]  #1: ffff0800e78800b8 (&vcpu->mutex){+.+.}-{3:3}, at: lock_all_vcpus+0x16c/0x2a0
[  328.212521]  #2: ffff07ffeee51e98 (&vcpu->mutex){+.+.}-{3:3}, at: lock_all_vcpus+0x16c/0x2a0
[  328.220991]  #3: ffff0800dc7d80b8 (&vcpu->mutex){+.+.}-{3:3}, at: lock_all_vcpus+0x16c/0x2a0
[  328.229463]  #4: ffff07ffe0c980b8 (&vcpu->mutex){+.+.}-{3:3}, at: lock_all_vcpus+0x16c/0x2a0
[  328.237934]  #5: ffff0800a3883c78 (&vcpu->mutex){+.+.}-{3:3}, at: lock_all_vcpus+0x16c/0x2a0
[  328.246405]  #6: ffff07fffbe480b8 (&vcpu->mutex){+.+.}-{3:3}, at: lock_all_vcpus+0x16c/0x2a0

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Message-ID: <20250512180407.659015-6-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Maxim Levitsky authored and Paolo Bonzini committed May 27, 2025
1 parent c560bc9 commit b586c5d
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Showing 6 changed files with 14 additions and 60 deletions.
3 changes: 0 additions & 3 deletions arch/arm64/include/asm/kvm_host.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1320,9 +1320,6 @@ int __init populate_sysreg_config(const struct sys_reg_desc *sr,
unsigned int idx);
int __init populate_nv_trap_config(void);

bool lock_all_vcpus(struct kvm *kvm);
void unlock_all_vcpus(struct kvm *kvm);

void kvm_calculate_traps(struct kvm_vcpu *vcpu);

/* MMIO helpers */
Expand Down
4 changes: 2 additions & 2 deletions arch/arm64/kvm/arch_timer.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1766,7 +1766,7 @@ int kvm_vm_ioctl_set_counter_offset(struct kvm *kvm,

mutex_lock(&kvm->lock);

if (lock_all_vcpus(kvm)) {
if (!kvm_trylock_all_vcpus(kvm)) {
set_bit(KVM_ARCH_FLAG_VM_COUNTER_OFFSET, &kvm->arch.flags);

/*
Expand All @@ -1778,7 +1778,7 @@ int kvm_vm_ioctl_set_counter_offset(struct kvm *kvm,
kvm->arch.timer_data.voffset = offset->counter_offset;
kvm->arch.timer_data.poffset = offset->counter_offset;

unlock_all_vcpus(kvm);
kvm_unlock_all_vcpus(kvm);
} else {
ret = -EBUSY;
}
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43 changes: 0 additions & 43 deletions arch/arm64/kvm/arm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1924,49 +1924,6 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
}
}

/* unlocks vcpus from @vcpu_lock_idx and smaller */
static void unlock_vcpus(struct kvm *kvm, int vcpu_lock_idx)
{
struct kvm_vcpu *tmp_vcpu;

for (; vcpu_lock_idx >= 0; vcpu_lock_idx--) {
tmp_vcpu = kvm_get_vcpu(kvm, vcpu_lock_idx);
mutex_unlock(&tmp_vcpu->mutex);
}
}

void unlock_all_vcpus(struct kvm *kvm)
{
lockdep_assert_held(&kvm->lock);

unlock_vcpus(kvm, atomic_read(&kvm->online_vcpus) - 1);
}

/* Returns true if all vcpus were locked, false otherwise */
bool lock_all_vcpus(struct kvm *kvm)
{
struct kvm_vcpu *tmp_vcpu;
unsigned long c;

lockdep_assert_held(&kvm->lock);

/*
* Any time a vcpu is in an ioctl (including running), the
* core KVM code tries to grab the vcpu->mutex.
*
* By grabbing the vcpu->mutex of all VCPUs we ensure that no
* other VCPUs can fiddle with the state while we access it.
*/
kvm_for_each_vcpu(c, tmp_vcpu, kvm) {
if (!mutex_trylock(&tmp_vcpu->mutex)) {
unlock_vcpus(kvm, c - 1);
return false;
}
}

return true;
}

static unsigned long nvhe_percpu_size(void)
{
return (unsigned long)CHOOSE_NVHE_SYM(__per_cpu_end) -
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4 changes: 2 additions & 2 deletions arch/arm64/kvm/vgic/vgic-init.c
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Original file line number Diff line number Diff line change
Expand Up @@ -88,7 +88,7 @@ int kvm_vgic_create(struct kvm *kvm, u32 type)
lockdep_assert_held(&kvm->lock);

ret = -EBUSY;
if (!lock_all_vcpus(kvm))
if (kvm_trylock_all_vcpus(kvm))
return ret;

mutex_lock(&kvm->arch.config_lock);
Expand Down Expand Up @@ -142,7 +142,7 @@ int kvm_vgic_create(struct kvm *kvm, u32 type)

out_unlock:
mutex_unlock(&kvm->arch.config_lock);
unlock_all_vcpus(kvm);
kvm_unlock_all_vcpus(kvm);
return ret;
}

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8 changes: 4 additions & 4 deletions arch/arm64/kvm/vgic/vgic-its.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1971,7 +1971,7 @@ static int vgic_its_attr_regs_access(struct kvm_device *dev,

mutex_lock(&dev->kvm->lock);

if (!lock_all_vcpus(dev->kvm)) {
if (kvm_trylock_all_vcpus(dev->kvm)) {
mutex_unlock(&dev->kvm->lock);
return -EBUSY;
}
Expand Down Expand Up @@ -2006,7 +2006,7 @@ static int vgic_its_attr_regs_access(struct kvm_device *dev,
}
out:
mutex_unlock(&dev->kvm->arch.config_lock);
unlock_all_vcpus(dev->kvm);
kvm_unlock_all_vcpus(dev->kvm);
mutex_unlock(&dev->kvm->lock);
return ret;
}
Expand Down Expand Up @@ -2676,7 +2676,7 @@ static int vgic_its_ctrl(struct kvm *kvm, struct vgic_its *its, u64 attr)

mutex_lock(&kvm->lock);

if (!lock_all_vcpus(kvm)) {
if (kvm_trylock_all_vcpus(kvm)) {
mutex_unlock(&kvm->lock);
return -EBUSY;
}
Expand All @@ -2698,7 +2698,7 @@ static int vgic_its_ctrl(struct kvm *kvm, struct vgic_its *its, u64 attr)

mutex_unlock(&its->its_lock);
mutex_unlock(&kvm->arch.config_lock);
unlock_all_vcpus(kvm);
kvm_unlock_all_vcpus(kvm);
mutex_unlock(&kvm->lock);
return ret;
}
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12 changes: 6 additions & 6 deletions arch/arm64/kvm/vgic/vgic-kvm-device.c
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Original file line number Diff line number Diff line change
Expand Up @@ -268,15 +268,15 @@ static int vgic_set_common_attr(struct kvm_device *dev,
return -ENXIO;
mutex_lock(&dev->kvm->lock);

if (!lock_all_vcpus(dev->kvm)) {
if (kvm_trylock_all_vcpus(dev->kvm)) {
mutex_unlock(&dev->kvm->lock);
return -EBUSY;
}

mutex_lock(&dev->kvm->arch.config_lock);
r = vgic_v3_save_pending_tables(dev->kvm);
mutex_unlock(&dev->kvm->arch.config_lock);
unlock_all_vcpus(dev->kvm);
kvm_unlock_all_vcpus(dev->kvm);
mutex_unlock(&dev->kvm->lock);
return r;
}
Expand Down Expand Up @@ -390,7 +390,7 @@ static int vgic_v2_attr_regs_access(struct kvm_device *dev,

mutex_lock(&dev->kvm->lock);

if (!lock_all_vcpus(dev->kvm)) {
if (kvm_trylock_all_vcpus(dev->kvm)) {
mutex_unlock(&dev->kvm->lock);
return -EBUSY;
}
Expand All @@ -415,7 +415,7 @@ static int vgic_v2_attr_regs_access(struct kvm_device *dev,

out:
mutex_unlock(&dev->kvm->arch.config_lock);
unlock_all_vcpus(dev->kvm);
kvm_unlock_all_vcpus(dev->kvm);
mutex_unlock(&dev->kvm->lock);

if (!ret && !is_write)
Expand Down Expand Up @@ -554,7 +554,7 @@ static int vgic_v3_attr_regs_access(struct kvm_device *dev,

mutex_lock(&dev->kvm->lock);

if (!lock_all_vcpus(dev->kvm)) {
if (kvm_trylock_all_vcpus(dev->kvm)) {
mutex_unlock(&dev->kvm->lock);
return -EBUSY;
}
Expand Down Expand Up @@ -611,7 +611,7 @@ static int vgic_v3_attr_regs_access(struct kvm_device *dev,

out:
mutex_unlock(&dev->kvm->arch.config_lock);
unlock_all_vcpus(dev->kvm);
kvm_unlock_all_vcpus(dev->kvm);
mutex_unlock(&dev->kvm->lock);

if (!ret && uaccess && !is_write) {
Expand Down

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