svm_vm_migrate_from() uses sev_lock_vcpus_for_migration() to lock all source and target vcpu->locks. Mark the nested subclasses to avoid false positives from lockdep. Warning example: ============================================ WARNING: possible recursive locking detected 5.17.0-dbg-DEV #15 Tainted: G O -------------------------------------------- sev_migrate_tes/18859 is trying to acquire lock: ffff8d672d484238 (&vcpu->mutex){+.+.}-{3:3}, at: sev_lock_vcpus_for_migration+0x7e/0x150 but task is already holding lock: ffff8d67703f81f8 (&vcpu->mutex){+.+.}-{3:3}, at: sev_lock_vcpus_for_migration+0x7e/0x150 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(&vcpu->mutex); lock(&vcpu->mutex); *** DEADLOCK *** May be due to missing lock nesting notation 3 locks held by sev_migrate_tes/18859: #0: ffff9302f91323b8 (&kvm->lock){+.+.}-{3:3}, at: sev_vm_move_enc_context_from+0x96/0x740 #1: ffff9302f906a3b8 (&kvm->lock/1){+.+.}-{3:3}, at: sev_vm_move_enc_context_from+0xae/0x740 #2: ffff8d67703f81f8 (&vcpu->mutex){+.+.}-{3:3}, at: sev_lock_vcpus_for_migration+0x7e/0x150 Fixes: b56639318bb2b ("KVM: SEV: Add support for SEV intra host migration") Reported-by: John Sperbeck<jsperbeck@xxxxxxxxxx> Suggested-by: David Rientjes <rientjes@xxxxxxxxxx> Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> Cc: kvm@xxxxxxxxxxxxxxx Cc: linux-kernel@xxxxxxxxxxxxxxx Signed-off-by: Peter Gonda <pgonda@xxxxxxxxxx> --- V3 * Updated signature to enum to self-document argument. * Updated comment as Seanjc@ suggested. Tested by running sev_migrate_tests with lockdep enabled. Before we see a warning from sev_lock_vcpus_for_migration(). After we get no warnings. --- arch/x86/kvm/svm/sev.c | 22 +++++++++++++++++----- 1 file changed, 17 insertions(+), 5 deletions(-) diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index 75fa6dd268f0..f66550ec8eaf 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -1591,14 +1591,26 @@ static void sev_unlock_two_vms(struct kvm *dst_kvm, struct kvm *src_kvm) atomic_set_release(&src_sev->migration_in_progress, 0); } +/* + * To suppress lockdep false positives, subclass all vCPU mutex locks by + * assigning even numbers to the source vCPUs and odd numbers to destination + * vCPUs based on the vCPU's index. + */ +enum sev_migration_role { + SEV_MIGRATION_SOURCE = 0, + SEV_MIGRATION_TARGET, + SEV_NR_MIGRATION_ROLES, +}; -static int sev_lock_vcpus_for_migration(struct kvm *kvm) +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(&vcpu->mutex)) + kvm_for_each_vcpu(i, vcpu, kvm) { + if (mutex_lock_killable_nested( + &vcpu->mutex, i * SEV_NR_MIGRATION_ROLES + role)) goto out_unlock; } @@ -1745,10 +1757,10 @@ int sev_vm_move_enc_context_from(struct kvm *kvm, unsigned int source_fd) charged = true; } - ret = sev_lock_vcpus_for_migration(kvm); + ret = sev_lock_vcpus_for_migration(kvm, SEV_MIGRATION_SOURCE); if (ret) goto out_dst_cgroup; - ret = sev_lock_vcpus_for_migration(source_kvm); + ret = sev_lock_vcpus_for_migration(source_kvm, SEV_MIGRATION_TARGET); if (ret) goto out_dst_vcpu; -- 2.35.1.1178.g4f1659d476-goog