On 2/10/21 5:46 PM, Halil Pasic wrote:
On Wed, 10 Feb 2021 17:05:48 -0500 Tony Krowiak akrowiak@linux.ibm.com wrote:
On 2/10/21 10:32 AM, Halil Pasic wrote:
On Wed, 10 Feb 2021 16:24:29 +0100 Halil Pasic pasic@linux.ibm.com wrote:
Maybe you could
- grab a reference to kvm while holding the lock
- call the mask handling functions with that kvm reference
- lock again, drop the reference, and do the rest of the processing?
I agree, matrix_mdev->kvm can go NULL any time and we are risking a null pointer dereference here.
Another idea would be to do
static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev) { struct kvm *kvm; mutex_lock(&matrix_dev->lock); if (matrix_mdev->kvm) { kvm = matrix_mdev->kvm; matrix_mdev->kvm = NULL; mutex_unlock(&matrix_dev->lock); kvm_arch_crypto_clear_masks(kvm); mutex_lock(&matrix_dev->lock); matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
s/matrix_mdev->kvm/kvm
vfio_ap_mdev_reset_queues(matrix_mdev->mdev); kvm_put_kvm(kvm); } mutex_unlock(&matrix_dev->lock);}
That way only one unset would actually do the unset and cleanup and every other invocation would bail out with only checking matrix_mdev->kvm.
But the problem with that is that we enable the the assign/unassign prematurely, which could interfere wit reset_queues(). Forget about it.
Not sure what you mean by this.
I mean because above I first do (1) matrix_mdev->kvm = NULL; and then do (2) vfio_ap_mdev_reset_queues(matrix_mdev->mdev); another thread could do static ssize_t unassign_adapter_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t count) { int ret; unsigned long apid; struct mdev_device *mdev = mdev_from_dev(dev); struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev); /* If the guest is running, disallow un-assignment of adapter */ if (matrix_mdev->kvm) return -EBUSY; ... } between (1) and (2), and we would not bail out with -EBUSY because !!kvm because of (1). That means we would change matrix_mdev->matrix and we would not reset the queues that correspond to the apid that was just removed, because by the time we do the reset_queues, the queues are not in the matrix_mdev->matrix any more.
Does that make sense?
Yes, it makes sense. I guess I didn't look closely at your suggestion when I said it was exactly what I implemented after agreeing with Connie. I had a slight difference in my implementation:
static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev) { struct kvm *kvm;
mutex_lock(&matrix_dev->lock);
if (matrix_mdev->kvm) { kvm = matrix_mdev->kvm; mutex_unlock(&matrix_dev->lock); kvm_arch_crypto_clear_masks(kvm); mutex_lock(&matrix_dev->lock); kvm->arch.crypto.pqap_hook = NULL; vfio_ap_mdev_reset_queues(matrix_mdev->mdev); matrix_mdev->kvm = NULL; kvm_put_kvm(kvm); }
mutex_unlock(&matrix_dev->lock); }
In your scenario, the unassignment would fail with -EBUSY because the matrix_mdev->kvm pointer would not have yet been cleared. The other problem with your implementation is that IRQ resources would not get cleared after the reset because the matrix_mdev->kvm pointer would be NULL at that time.