On 7/15/21 9:44 AM, Halil Pasic wrote:
On Wed, 7 Jul 2021 11:41:56 -0400
Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
First sorry for being this late with having a more serious look at the
code.
@@ -270,6 +270,9 @@ static struct ap_queue_status vfio_ap_irq_enable(struct vfio_ap_queue *q,
* We take the matrix_dev lock to ensure serialization on queues and
* mediated device access.
*
+ * Note: This function must be called with a read lock held on
+ * vcpu->kvm->arch.crypto.pqap_hook_rwsem.
+ *
That is a fine synchronization for the pqap_hook, but I don't think it
is sufficient for everything.
* Return 0 if we could handle the request inside KVM.
* otherwise, returns -EOPNOTSUPP to let QEMU handle the fault.
*/
@@ -287,22 +290,12 @@ static int handle_pqap(struct kvm_vcpu *vcpu)
return -EOPNOTSUPP;
apqn = vcpu->run->s.regs.gprs[0] & 0xffff;
- mutex_lock(&matrix_dev->lock);
Here you drop a matrix_dev->lock critical section. And then
you do all the interesting stuff. E.g.
q = vfio_ap_get_queue(matrix_mdev, apqn);
and
vfio_ap_irq_enable(q, status & 0x07, vcpu->run->s.regs.gprs[2]);.
Since in vfio_ap_get_queue() we do the check if the queue belongs
to the given guest, and examine the matrix (apm, aqm) I suppose
that needs to be done holding a lock that protects the matrix,
and to my best knowledge this is still matrix_dev->lock. It would
probably make sense to convert matrix_dev->lock into an rw_semaphore,
or to introduce a some new rwlock which protects less state in the
future, but right now AFAICT it is still matrix_dev->lock.
So I don't think this patch should pass review.
Good catch. In an earlier patch review, Jason G suggested locking the
kvm->lock
mutex outside of the kvm_arch_crypto_set_masks() and
kvm_arch_crypto_clear_masks()
functions to resolve the lockdep splat resulting from locking the
matrix_dev->lock
mutex prior to the kvm->lock mutex. I believe this will allow me to remove
the kvm_busy/wait queue scenario without introducing a new rwsem.
Regards,
Halil
if (!vcpu->kvm->arch.crypto.pqap_hook)
goto out_unlock;
matrix_mdev = container_of(vcpu->kvm->arch.crypto.pqap_hook,
struct ap_matrix_mdev, pqap_hook);
- /*
- * If the KVM pointer is in the process of being set, wait until the
- * process has completed.
- */
- wait_event_cmd(matrix_mdev->wait_for_kvm,
- !matrix_mdev->kvm_busy,
- mutex_unlock(&matrix_dev->lock),
- mutex_lock(&matrix_dev->lock));
-
/* If the there is no guest using the mdev, there is nothing to do */
if (!matrix_mdev->kvm)
goto out_unlock;
