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From: Sahil Siddiq <icegambit91@gmail.com>
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To: eperezma@redhat.com,
sgarzare@redhat.com
Cc: mst@redhat.com,
qemu-devel@nongnu.org,
sahilcdq@proton.me
Subject: [RFC v5 7/7] vdpa: Support setting vring_base for packed SVQ
Date: Mon, 24 Mar 2025 19:29:21 +0530
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This commit is the first in a series to add support for packed
virtqueues in vhost_shadow_virtqueue.
Linux commit 1225c216d954 ("vp_vdpa: allow set vq state to initial
state after reset") enabled the vp_vdpa driver to set the vq state to
the device's initial state. This works differently for split and packed
vqs.
With shadow virtqueues enabled, vhost-vdpa sets the vring base using
the VHOST_SET_VRING_BASE ioctl. The payload (vhost_vring_state)
differs for split and packed vqs. The implementation in QEMU currently
uses the payload required for split vqs (i.e., the num field of
vhost_vring_state is set to 0). The kernel throws EOPNOTSUPP when this
payload is used with packed vqs.
This patch sets the num field in the payload appropriately so vhost-vdpa
(with the vp_vdpa driver) can use packed SVQs.
Link: https://lists.nongnu.org/archive/html/qemu-devel/2024-10/msg05106.html
Link: https://lore.kernel.org/r/20210602021536.39525-4-jasowang@redhat.com
Link: 1225c216d954 ("vp_vdpa: allow set vq state to initial state after res=
et")
Signed-off-by: Sahil Siddiq <sahilcdq@proton.me>
Acked-by: Eugenio P=C3=A9rez <eperezma@redhat.com>
---
Changes from v4 -> v5:
- Initially commit #5 in v4.
- Fix coding style of commit block as stated by checkpatch.pl.
hw/virtio/vhost-vdpa.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
index 58c8931d89..0625e349b3 100644
--- a/hw/virtio/vhost-vdpa.c
+++ b/hw/virtio/vhost-vdpa.c
@@ -1265,6 +1265,21 @@ static bool vhost_vdpa_svq_setup(struct vhost_dev *d=
ev,
};
int r;
=20
+ /*
+ * In Linux, the upper 16 bits of s.num is encoded as
+ * the last used idx while the lower 16 bits is encoded
+ * as the last avail idx when using packed vqs. The most
+ * significant bit for each idx represents the counter
+ * and should be set in both cases while the remaining
+ * bits are cleared.
+ */
+ if (virtio_vdev_has_feature(dev->vdev, VIRTIO_F_RING_PACKED)) {
+ uint32_t last_avail_idx =3D 0 | (1 << VRING_PACKED_EVENT_F_WRAP_CT=
R);
+ uint32_t last_used_idx =3D 0 | (1 << VRING_PACKED_EVENT_F_WRAP_CTR=
);
+
+ s.num =3D (last_used_idx << 16) | last_avail_idx;
+ }
+
r =3D vhost_vdpa_set_dev_vring_base(dev, &s);
if (unlikely(r)) {
error_setg_errno(errp, -r, "Cannot set vring base");
--=20
2.48.1