[PATCH v4 2/5] arm64: KVM: use mutex_trylock_nest_lock when locking all vCPUs

[Maxim Levitsky <mlevitsk@redhat.com>]

Use mutex_trylock_nest_lock instead of mutex_trylock when locking all vCPUs
of a VM, to avoid triggering a lockdep warning, if 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

Since the locking of all vCPUs is a primitive that can be useful in other
architectures that are supported by KVM, also move the code to kvm_main.c

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
 arch/arm64/include/asm/kvm_host.h     |  3 --
 arch/arm64/kvm/arch_timer.c           |  4 +--
 arch/arm64/kvm/arm.c                  | 43 ---------------------------
 arch/arm64/kvm/vgic/vgic-init.c       |  4 +--
 arch/arm64/kvm/vgic/vgic-its.c        |  8 ++---
 arch/arm64/kvm/vgic/vgic-kvm-device.c | 12 ++++----
 include/linux/kvm_host.h              |  3 ++
 virt/kvm/kvm_main.c                   | 34 +++++++++++++++++++++
 8 files changed, 51 insertions(+), 60 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index e98cfe7855a6..96ce0b01a61e 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -1263,9 +1263,6 @@ 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 */
diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
index 5133dcbfe9f7..fdbc8beec930 100644
--- a/arch/arm64/kvm/arch_timer.c
+++ b/arch/arm64/kvm/arch_timer.c
@@ -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);
 
 		/*
@@ -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;
 	}
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 68fec8c95fee..d31f42a71bdc 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1914,49 +1914,6 @@ 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) -
diff --git a/arch/arm64/kvm/vgic/vgic-init.c b/arch/arm64/kvm/vgic/vgic-init.c
index 1f33e71c2a73..6a426d403a6b 100644
--- a/arch/arm64/kvm/vgic/vgic-init.c
+++ b/arch/arm64/kvm/vgic/vgic-init.c
@@ -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);
@@ -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;
 }
 
diff --git a/arch/arm64/kvm/vgic/vgic-its.c b/arch/arm64/kvm/vgic/vgic-its.c
index fb96802799c6..7454388e3646 100644
--- a/arch/arm64/kvm/vgic/vgic-its.c
+++ b/arch/arm64/kvm/vgic/vgic-its.c
@@ -1999,7 +1999,7 @@ 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;
 	}
@@ -2034,7 +2034,7 @@ 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;
 }
@@ -2704,7 +2704,7 @@ 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;
 	}
@@ -2726,7 +2726,7 @@ 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;
 }
diff --git a/arch/arm64/kvm/vgic/vgic-kvm-device.c b/arch/arm64/kvm/vgic/vgic-kvm-device.c
index 359094f68c23..f9ae790163fb 100644
--- a/arch/arm64/kvm/vgic/vgic-kvm-device.c
+++ b/arch/arm64/kvm/vgic/vgic-kvm-device.c
@@ -268,7 +268,7 @@ 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;
 			}
@@ -276,7 +276,7 @@ static int vgic_set_common_attr(struct kvm_device *dev,
 			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;
 		}
@@ -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;
 	}
@@ -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)
@@ -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;
 	}
@@ -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) {
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 1dedc421b3e3..10d6652c7aa0 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1015,6 +1015,9 @@ static inline struct kvm_vcpu *kvm_get_vcpu_by_id(struct kvm *kvm, int id)
 
 void kvm_destroy_vcpus(struct kvm *kvm);
 
+int kvm_trylock_all_vcpus(struct kvm *kvm);
+void kvm_unlock_all_vcpus(struct kvm *kvm);
+
 void vcpu_load(struct kvm_vcpu *vcpu);
 void vcpu_put(struct kvm_vcpu *vcpu);
 
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 69782df3617f..834f08dfa24c 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1368,6 +1368,40 @@ static int kvm_vm_release(struct inode *inode, struct file *filp)
 	return 0;
 }
 
+/*
+ * Try to lock all of the VM's vCPUs.
+ * Assumes that the kvm->lock is held.
+ */
+int kvm_trylock_all_vcpus(struct kvm *kvm)
+{
+	struct kvm_vcpu *vcpu;
+	unsigned long i, j;
+
+	kvm_for_each_vcpu(i, vcpu, kvm)
+		if (!mutex_trylock_nest_lock(&vcpu->mutex, &kvm->lock))
+			goto out_unlock;
+	return 0;
+
+out_unlock:
+	kvm_for_each_vcpu(j, vcpu, kvm) {
+		if (i == j)
+			break;
+		mutex_unlock(&vcpu->mutex);
+	}
+	return -EINTR;
+}
+EXPORT_SYMBOL_GPL(kvm_trylock_all_vcpus);
+
+void kvm_unlock_all_vcpus(struct kvm *kvm)
+{
+	struct kvm_vcpu *vcpu;
+	unsigned long i;
+
+	kvm_for_each_vcpu(i, vcpu, kvm)
+		mutex_unlock(&vcpu->mutex);
+}
+EXPORT_SYMBOL_GPL(kvm_unlock_all_vcpus);
+
 /*
  * Allocation size is twice as large as the actual dirty bitmap size.
  * See kvm_vm_ioctl_get_dirty_log() why this is needed.
-- 
2.46.0


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