On 2/10/21 5:46 PM, Halil Pasic wrote:
On Wed, 10 Feb 2021 17:05:48 -0500
Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
On 2/10/21 10:32 AM, Halil Pasic wrote:
On Wed, 10 Feb 2021 16:24:29 +0100
Halil Pasic <pasic@xxxxxxxxxxxxx> 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.
