KVM: SEV: Mark nested locking of kvm->lock

Both source and dest vms' kvm->locks are held in sev_lock_two_vms.
Mark one with a different subtype to avoid false positives from lockdep.

Fixes: c9d61dc (KVM: SEV: accept signals in sev_lock_two_vms)
Reported-by: Yiru Xu <xyru1999@gmail.com>
Tested-by: Jinrong Liang <cloudliang@tencent.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Message-Id: <1641364863-26331-1-git-send-email-wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/sev.c

@@ -1565,7 +1565,7 @@ static int sev_lock_two_vms(struct kvm *dst_kvm, struct kvm *src_kvm)
  r = -EINTR;
  if (mutex_lock_killable(&dst_kvm->lock))
  goto release_src;
- if (mutex_lock_killable(&src_kvm->lock))
+ if (mutex_lock_killable_nested(&src_kvm->lock, SINGLE_DEPTH_NESTING))
  goto unlock_dst;
  return 0;