On Mon, Jun 05, 2023 at 08:41:54AM -0400, Michael S. Tsirkin wrote:
On Mon, Jun 05, 2023 at 01:06:44PM +0200, Stefano Garzarella wrote:
vhost-vdpa IOCTLs (eg. VHOST_GET_VRING_BASE, VHOST_SET_VRING_BASE)
don't support packed virtqueue well yet, so let's filter the
VIRTIO_F_RING_PACKED feature for now in vhost_vdpa_get_features().
This way, even if the device supports it, we don't risk it being
negotiated, then the VMM is unable to set the vring state properly.
Fixes: 4c8cf31885f6 ("vhost: introduce vDPA-based backend")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
---
Notes:
This patch should be applied before the "[PATCH v2 0/3] vhost_vdpa:
better PACKED support" series [1] and backported in stable branches.
We can revert it when we are sure that everything is working with
packed virtqueues.
Thanks,
Stefano
[1] https://lore.kernel.org/virtualization/20230424225031.18947-1-shannon.nelson@xxxxxxx/
I'm a bit lost here. So why am I merging "better PACKED support" then?
To really support packed virtqueue with vhost-vdpa, at that point we
would also have to revert this patch.
I wasn't sure if you wanted to queue the series for this merge window.
In that case do you think it is better to send this patch only for
stable branches?
Does this patch make them a NOP?
Yep, after applying the "better PACKED support" series and being sure
that the IOCTLs of vhost-vdpa support packed virtqueue, we should revert
this patch.
Let me know if you prefer a different approach.
I'm concerned that QEMU uses vhost-vdpa IOCTLs thinking that the kernel
interprets them the right way, when it does not.
Thanks,
Stefano
drivers/vhost/vdpa.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index 8c1aefc865f0..ac2152135b23 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -397,6 +397,12 @@ static long vhost_vdpa_get_features(struct vhost_vdpa *v, u64 __user *featurep)
features = ops->get_device_features(vdpa);
+ /*
+ * IOCTLs (eg. VHOST_GET_VRING_BASE, VHOST_SET_VRING_BASE) don't support
+ * packed virtqueue well yet, so let's filter the feature for now.
+ */
+ features &= ~BIT_ULL(VIRTIO_F_RING_PACKED);
+
if (copy_to_user(featurep, &features, sizeof(features)))
return -EFAULT;
base-commit: 9561de3a55bed6bdd44a12820ba81ec416e705a7
--
2.40.1
