On 28/03/2019 21:46, Tony Krowiak wrote:
On 3/22/19 10:43 AM, Pierre Morel wrote:
To be able to use the VFIO interface to facilitate the
mediated device memory pinning/unpinning we need to register
a notifier for IOMMU.
While we will start to pin one guest page for the interrupt indicator
byte, this is still ok with ballooning as this page will never be
used by the guest virtio-balloon driver.
So the pinned page will never be freed. And even a broken guest does
so, that would not impact the host as the original page is still
in control by vfio.
I apologize, but I do not understand what you are saying in the second
sentence of the paragraph above. Why will the pinned page never be
freed?
Because it is in use by the guest's kernel as a notification information
byte for the original PQAP AQIC.
I understand that the pinned page is under the control of vfio
until it is freed, but have no idea what you mean by "and even a broken
guest does so"? A broken guest does what? Can you please reword this so
it makes more sense?
A broken guest could free the page used for the NIB. What is obviously
wrong.
Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
Reviewed-by: Cornelia Huck <cohuck@xxxxxxxxxx>
---
drivers/s390/crypto/vfio_ap_ops.c | 38
+++++++++++++++++++++++++++++++++++
drivers/s390/crypto/vfio_ap_private.h | 2 ++
2 files changed, 40 insertions(+)
diff --git a/drivers/s390/crypto/vfio_ap_ops.c
b/drivers/s390/crypto/vfio_ap_ops.c
index bdb36e0..3478499 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -787,6 +787,35 @@ static const struct attribute_group
*vfio_ap_mdev_attr_groups[] = {
NULL
};
+/**
+ * vfio_ap_mdev_iommu_notifier: IOMMU notifier callback
+ *
+ * @nb: The notifier block
+ * @action: Action to be taken
+ * @data: data associated with the request
+ *
+ * For an UNMAP request, unpin the guest IOVA (the NIB guest address we
+ * pinned before). Other requests are ignored.
+ *
+ */
+static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb,
+ unsigned long action, void *data)
+{
+ struct ap_matrix_mdev *matrix_mdev;
+
+ matrix_mdev = container_of(nb, struct ap_matrix_mdev,
iommu_notifier);
+
I don't understand why we registered this notifier. I may be wrong, but
AFAIU, this notifier will be invoked only when the VFIO_IOMMU_UNMAP_DMA
ioctl is called from userspace. I did an experiment and inserted some
printf's to see if this ever gets called and verified it does not. Maybe
you have a good reason of which I'm not aware. Can you enlighten me
here?
The vfio_iommu_type1 pin page requires a notifier.
Regards,
Pierre
--
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany
