[PATCH v2 2/4] KVM: x86: move sev_lock/unlock_vcpus_for_migration to kvm_main.c

Maxim Levitsky
2025-04-09T01:42:07Z

Move sev_lock/unlock_vcpus_for_migration to kvm_main and call the
new functions the kvm_lock_all_vcpus/kvm_unlock_all_vcpus
and kvm_lock_all_vcpus_nested.

This code allows to lock all vCPUs without triggering lockdep warning
about reaching MAX_LOCK_DEPTH depth by coercing the lockdep into
thinking that we release all the locks other than vcpu'0 lock
immediately after we take them.

No functional change intended.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
arch/x86/kvm/svm/sev.c | 65 +++---------------------------------
include/linux/kvm_host.h | 6 ++++
virt/kvm/kvm_main.c | 71 ++++++++++++++++++++++++++++++++++++++++
3 files changed, 81 insertions(+), 61 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 0bc708ee2788..7adc54b1f741 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1889,63 +1889,6 @@ enum sev_migration_role {
SEV_NR_MIGRATION_ROLES,
};

-static int sev_lock_vcpus_for_migration(struct kvm *kvm,
- enum sev_migration_role role)
-{
- struct kvm_vcpu *vcpu;
- unsigned long i, j;
-
- kvm_for_each_vcpu(i, vcpu, kvm) {
- if (mutex_lock_killable_nested(&vcpu->mutex, role))
- goto out_unlock;
-
-#ifdef CONFIG_PROVE_LOCKING
- if (!i)
- /*
- * Reset the role to one that avoids colliding with
- * the role used for the first vcpu mutex.
- */
- role = SEV_NR_MIGRATION_ROLES;
- else
- mutex_release(&vcpu->mutex.dep_map, _THIS_IP_);
-#endif
- }
-
- return 0;
-
-out_unlock:
-
- kvm_for_each_vcpu(j, vcpu, kvm) {
- if (i == j)
- break;
-
-#ifdef CONFIG_PROVE_LOCKING
- if (j)
- mutex_acquire(&vcpu->mutex.dep_map, role, 0, _THIS_IP_);
-#endif
-
- mutex_unlock(&vcpu->mutex);
- }
- return -EINTR;
-}
-
-static void sev_unlock_vcpus_for_migration(struct kvm *kvm)
-{
- struct kvm_vcpu *vcpu;
- unsigned long i;
- bool first = true;
-
- kvm_for_each_vcpu(i, vcpu, kvm) {
- if (first)
- first = false;
- else
- mutex_acquire(&vcpu->mutex.dep_map,
- SEV_NR_MIGRATION_ROLES, 0, _THIS_IP_);
-
- mutex_unlock(&vcpu->mutex);
- }
-}
-
static void sev_migrate_from(struct kvm *dst_kvm, struct kvm *src_kvm)
{
struct kvm_sev_info *dst = to_kvm_sev_info(dst_kvm);
@@ -2083,10 +2026,10 @@ int sev_vm_move_enc_context_from(struct kvm *kvm, unsigned int source_fd)
charged = true;
}

- ret = sev_lock_vcpus_for_migration(kvm, SEV_MIGRATION_SOURCE);
+ ret = kvm_lock_all_vcpus_nested(kvm, false, SEV_MIGRATION_SOURCE);
if (ret)
goto out_dst_cgroup;
- ret = sev_lock_vcpus_for_migration(source_kvm, SEV_MIGRATION_TARGET);
+ ret = kvm_lock_all_vcpus_nested(source_kvm, false, SEV_MIGRATION_TARGET);
if (ret)
goto out_dst_vcpu;

@@ -2100,9 +2043,9 @@ int sev_vm_move_enc_context_from(struct kvm *kvm, unsigned int source_fd)
ret = 0;

out_source_vcpu:
- sev_unlock_vcpus_for_migration(source_kvm);
+ kvm_unlock_all_vcpus(source_kvm);
out_dst_vcpu:
- sev_unlock_vcpus_for_migration(kvm);
+ kvm_unlock_all_vcpus(kvm);
out_dst_cgroup:
/* Operates on the source on success, on the destination on failure. */
if (charged)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 1dedc421b3e3..30cf28bf5c80 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1015,6 +1015,12 @@ static inline struct kvm_vcpu *kvm_get_vcpu_by_id(struct kvm *kvm, int id)

void kvm_destroy_vcpus(struct kvm *kvm);

+int kvm_lock_all_vcpus_nested(struct kvm *kvm, bool trylock, unsigned int role);
+void kvm_unlock_all_vcpus(struct kvm *kvm);
+
+#define kvm_lock_all_vcpus(kvm, trylock) \
+ kvm_lock_all_vcpus_nested(kvm, trylock, 0)
+
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..71c0d8c35b4b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1368,6 +1368,77 @@ static int kvm_vm_release(struct inode *inode, struct file *filp)
return 0;
}

+
+/*
+ * Lock all VM vCPUs.
+ * Can be used nested (to lock vCPUS of two VMs for example)
+ */
+int kvm_lock_all_vcpus_nested(struct kvm *kvm, bool trylock, unsigned int role)
+{
+ struct kvm_vcpu *vcpu;
+ unsigned long i, j;
+
+ lockdep_assert_held(&kvm->lock);
+
+ kvm_for_each_vcpu(i, vcpu, kvm) {
+
+ if (trylock && !mutex_trylock_nested(&vcpu->mutex, role))
+ goto out_unlock;
+ else if (!trylock && mutex_lock_killable_nested(&vcpu->mutex, role))
+ goto out_unlock;
+
+#ifdef CONFIG_PROVE_LOCKING
+ if (!i)
+ /*
+ * Reset the role to one that avoids colliding with
+ * the role used for the first vcpu mutex.
+ */
+ role = MAX_LOCK_DEPTH - 1;
+ else
+ mutex_release(&vcpu->mutex.dep_map, _THIS_IP_);
+#endif
+ }
+
+ return 0;
+
+out_unlock:
+
+ kvm_for_each_vcpu(j, vcpu, kvm) {
+ if (i == j)
+ break;
+
+#ifdef CONFIG_PROVE_LOCKING
+ if (j)
+ mutex_acquire(&vcpu->mutex.dep_map, role, 0, _THIS_IP_);
+#endif
+
+ mutex_unlock(&vcpu->mutex);
+ }
+ return -EINTR;
+}
+EXPORT_SYMBOL_GPL(kvm_lock_all_vcpus_nested);
+
+void kvm_unlock_all_vcpus(struct kvm *kvm)
+{
+ struct kvm_vcpu *vcpu;
+ unsigned long i;
+ bool first = true;
+
+ lockdep_assert_held(&kvm->lock);
+
+ kvm_for_each_vcpu(i, vcpu, kvm) {
+ if (first)
+ first = false;
+ else
+ mutex_acquire(&vcpu->mutex.dep_map,
+ MAX_LOCK_DEPTH - 1, 0, _THIS_IP_);
+
+ 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.
--
2.26.3