KVM: SEV: cleanup locking for KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM

Encapsulate the handling of the migration_in_progress flag for both VMs in
two functions sev_lock_two_vms and sev_unlock_two_vms.  It does not matter
if KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM locks the destination struct kvm a bit
later, and this change 1) keeps the cleanup chain of labels smaller 2)
makes it possible for KVM_CAP_VM_COPY_ENC_CONTEXT_FROM to reuse the logic.

Cc: Peter Gonda <pgonda@google.com>
Cc: Sean Christopherson <seanjc@google.com>
Message-Id: <20211123005036.2954379-6-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 75955beb3770f2aa22035031e6e933029c4e9548..8902b018fc18e8b7e9f460bf924775a765f32dc1 100644 (file)
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1543,28 +1543,40 @@ static bool is_cmd_allowed_from_mirror(u32 cmd_id)
        return false;
 }
 
-static int sev_lock_for_migration(struct kvm *kvm)
+static int sev_lock_two_vms(struct kvm *dst_kvm, struct kvm *src_kvm)
 {
-       struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
+       struct kvm_sev_info *dst_sev = &to_kvm_svm(dst_kvm)->sev_info;
+       struct kvm_sev_info *src_sev = &to_kvm_svm(src_kvm)->sev_info;
+
+       if (dst_kvm == src_kvm)
+               return -EINVAL;
 
        /*
-        * Bail if this VM is already involved in a migration to avoid deadlock
-        * between two VMs trying to migrate to/from each other.
+        * Bail if these VMs are already involved in a migration to avoid
+        * deadlock between two VMs trying to migrate to/from each other.
         */
-       if (atomic_cmpxchg_acquire(&sev->migration_in_progress, 0, 1))
+       if (atomic_cmpxchg_acquire(&dst_sev->migration_in_progress, 0, 1))
                return -EBUSY;
 
-       mutex_lock(&kvm->lock);
+       if (atomic_cmpxchg_acquire(&src_sev->migration_in_progress, 0, 1)) {
+               atomic_set_release(&dst_sev->migration_in_progress, 0);
+               return -EBUSY;
+       }
 
+       mutex_lock(&dst_kvm->lock);
+       mutex_lock(&src_kvm->lock);
        return 0;
 }
 
-static void sev_unlock_after_migration(struct kvm *kvm)
+static void sev_unlock_two_vms(struct kvm *dst_kvm, struct kvm *src_kvm)
 {
-       struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
+       struct kvm_sev_info *dst_sev = &to_kvm_svm(dst_kvm)->sev_info;
+       struct kvm_sev_info *src_sev = &to_kvm_svm(src_kvm)->sev_info;
 
-       mutex_unlock(&kvm->lock);
-       atomic_set_release(&sev->migration_in_progress, 0);
+       mutex_unlock(&dst_kvm->lock);
+       mutex_unlock(&src_kvm->lock);
+       atomic_set_release(&dst_sev->migration_in_progress, 0);
+       atomic_set_release(&src_sev->migration_in_progress, 0);
 }
 
 
@@ -1665,15 +1677,6 @@ int svm_vm_migrate_from(struct kvm *kvm, unsigned int source_fd)
        bool charged = false;
        int ret;
 
-       ret = sev_lock_for_migration(kvm);
-       if (ret)
-               return ret;
-
-       if (sev_guest(kvm)) {
-               ret = -EINVAL;
-               goto out_unlock;
-       }
-
        source_kvm_file = fget(source_fd);
        if (!file_is_kvm(source_kvm_file)) {
                ret = -EBADF;
@@ -1681,13 +1684,13 @@ int svm_vm_migrate_from(struct kvm *kvm, unsigned int source_fd)
        }
 
        source_kvm = source_kvm_file->private_data;
-       ret = sev_lock_for_migration(source_kvm);
+       ret = sev_lock_two_vms(kvm, source_kvm);
        if (ret)
                goto out_fput;
 
-       if (!sev_guest(source_kvm)) {
+       if (sev_guest(kvm) || !sev_guest(source_kvm)) {
                ret = -EINVAL;
-               goto out_source;
+               goto out_unlock;
        }
 
        src_sev = &to_kvm_svm(source_kvm)->sev_info;
@@ -1727,13 +1730,11 @@ out_dst_cgroup:
                sev_misc_cg_uncharge(cg_cleanup_sev);
        put_misc_cg(cg_cleanup_sev->misc_cg);
        cg_cleanup_sev->misc_cg = NULL;
-out_source:
-       sev_unlock_after_migration(source_kvm);
+out_unlock:
+       sev_unlock_two_vms(kvm, source_kvm);
 out_fput:
        if (source_kvm_file)
                fput(source_kvm_file);
-out_unlock:
-       sev_unlock_after_migration(kvm);
        return ret;
 }