This is the first patch in a series to add support for packed
virtqueues in vhost_shadow_virtqueue. This patch implements the
insertion of available buffers in the descriptor area. It takes
into account descriptor chains, but does not consider indirect
descriptors.

Signed-off-by: Sahil Siddiq <sahilcdq@proton.me>
---
Changes v1 -> v2:
* Split commit from RFC v1 into two commits.
* vhost-shadow-virtqueue.c
  (vhost_svq_add_packed):
  - Merge with "vhost_svq_vring_write_descs_packed()"
  - Remove "num == 0" check

 hw/virtio/vhost-shadow-virtqueue.c | 93 +++++++++++++++++++++++++++++-
 1 file changed, 92 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index fc5f408f77..c7b7e0c477 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -217,6 +217,91 @@ static bool vhost_svq_add_split(VhostShadowVirtqueue *svq,
     return true;
 }
 
+static bool vhost_svq_add_packed(VhostShadowVirtqueue *svq,
+                                const struct iovec *out_sg, size_t out_num,
+                                const struct iovec *in_sg, size_t in_num,
+                                unsigned *head)
+{
+    bool ok;
+    uint16_t head_flags = 0;
+    g_autofree hwaddr *sgs = g_new(hwaddr, out_num + in_num);
+
+    *head = svq->vring_packed.next_avail_idx;
+
+    /* We need some descriptors here */
+    if (unlikely(!out_num && !in_num)) {
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "Guest provided element with no descriptors");
+        return false;
+    }
+
+    uint16_t id, curr, i;
+    unsigned n;
+    struct vring_packed_desc *descs = svq->vring_packed.vring.desc;
+
+    i = *head;
+    id = svq->free_head;
+    curr = id;
+
+    size_t num = out_num + in_num;
+
+    ok = vhost_svq_translate_addr(svq, sgs, out_sg, out_num);
+    if (unlikely(!ok)) {
+        return false;
+    }
+
+    ok = vhost_svq_translate_addr(svq, sgs + out_num, in_sg, in_num);
+    if (unlikely(!ok)) {
+        return false;
+    }
+
+    /* Write descriptors to SVQ packed vring */
+    for (n = 0; n < num; n++) {
+        uint16_t flags = cpu_to_le16(svq->vring_packed.avail_used_flags |
+                                     (n < out_num ? 0 : VRING_DESC_F_WRITE) |
+                                     (n + 1 == num ? 0 : VRING_DESC_F_NEXT));
+        if (i == *head) {
+            head_flags = flags;
+        } else {
+            descs[i].flags = flags;
+        }
+
+        descs[i].addr = cpu_to_le64(sgs[n]);
+        descs[i].id = id;
+        if (n < out_num) {
+            descs[i].len = cpu_to_le32(out_sg[n].iov_len);
+        } else {
+            descs[i].len = cpu_to_le32(in_sg[n - out_num].iov_len);
+        }
+
+        curr = cpu_to_le16(svq->desc_next[curr]);
+
+        if (++i >= svq->vring_packed.vring.num) {
+            i = 0;
+            svq->vring_packed.avail_used_flags ^=
+                    1 << VRING_PACKED_DESC_F_AVAIL |
+                    1 << VRING_PACKED_DESC_F_USED;
+        }
+    }
+
+    if (i <= *head) {
+        svq->vring_packed.avail_wrap_counter ^= 1;
+    }
+
+    svq->vring_packed.next_avail_idx = i;
+    svq->free_head = curr;
+
+    /*
+     * A driver MUST NOT make the first descriptor in the list
+     * available before all subsequent descriptors comprising
+     * the list are made available.
+     */
+    smp_wmb();
+    svq->vring_packed.vring.desc[*head].flags = head_flags;
+
+    return true;
+}
+
 static void vhost_svq_kick(VhostShadowVirtqueue *svq)
 {
     bool needs_kick;
@@ -258,7 +343,13 @@ int vhost_svq_add(VhostShadowVirtqueue *svq, const struct iovec *out_sg,
         return -ENOSPC;
     }
 
-    ok = vhost_svq_add_split(svq, out_sg, out_num, in_sg, in_num, &qemu_head);
+    if (virtio_vdev_has_feature(svq->vdev, VIRTIO_F_RING_PACKED)) {
+        ok = vhost_svq_add_packed(svq, out_sg, out_num,
+                                  in_sg, in_num, &qemu_head);
+    } else {
+        ok = vhost_svq_add_split(svq, out_sg, out_num,
+                                 in_sg, in_num, &qemu_head);
+    }
     if (unlikely(!ok)) {
         return -EINVAL;
     }
-- 
2.45.2

On Fri, Jul 26, 2024 at 11:58 AM Sahil Siddiq <icegambit91@gmail.com> wrote:
>
> This is the first patch in a series to add support for packed
> virtqueues in vhost_shadow_virtqueue. This patch implements the
> insertion of available buffers in the descriptor area. It takes
> into account descriptor chains, but does not consider indirect
> descriptors.
>
> Signed-off-by: Sahil Siddiq <sahilcdq@proton.me>
> ---
> Changes v1 -> v2:
> * Split commit from RFC v1 into two commits.
> * vhost-shadow-virtqueue.c
>   (vhost_svq_add_packed):
>   - Merge with "vhost_svq_vring_write_descs_packed()"
>   - Remove "num == 0" check
>
>  hw/virtio/vhost-shadow-virtqueue.c | 93 +++++++++++++++++++++++++++++-
>  1 file changed, 92 insertions(+), 1 deletion(-)
>
> diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
> index fc5f408f77..c7b7e0c477 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.c
> +++ b/hw/virtio/vhost-shadow-virtqueue.c
> @@ -217,6 +217,91 @@ static bool vhost_svq_add_split(VhostShadowVirtqueue *svq,
>      return true;
>  }
>
> +static bool vhost_svq_add_packed(VhostShadowVirtqueue *svq,
> +                                const struct iovec *out_sg, size_t out_num,
> +                                const struct iovec *in_sg, size_t in_num,
> +                                unsigned *head)
> +{
> +    bool ok;
> +    uint16_t head_flags = 0;
> +    g_autofree hwaddr *sgs = g_new(hwaddr, out_num + in_num);
> +
> +    *head = svq->vring_packed.next_avail_idx;
> +
> +    /* We need some descriptors here */
> +    if (unlikely(!out_num && !in_num)) {
> +        qemu_log_mask(LOG_GUEST_ERROR,
> +                      "Guest provided element with no descriptors");
> +        return false;
> +    }
> +
> +    uint16_t id, curr, i;
> +    unsigned n;
> +    struct vring_packed_desc *descs = svq->vring_packed.vring.desc;
> +
> +    i = *head;
> +    id = svq->free_head;
> +    curr = id;
> +
> +    size_t num = out_num + in_num;
> +
> +    ok = vhost_svq_translate_addr(svq, sgs, out_sg, out_num);
> +    if (unlikely(!ok)) {
> +        return false;
> +    }
> +
> +    ok = vhost_svq_translate_addr(svq, sgs + out_num, in_sg, in_num);
> +    if (unlikely(!ok)) {
> +        return false;
> +    }
> +

(sorry I missed this from the RFC v1) I think all of the above should
be in the caller, isn't it? It is duplicated with split.

Also, declarations should be at the beginning of blocks per QEMU
coding style [1].

The rest looks good to me by visual inspection.

> +    /* Write descriptors to SVQ packed vring */
> +    for (n = 0; n < num; n++) {
> +        uint16_t flags = cpu_to_le16(svq->vring_packed.avail_used_flags |
> +                                     (n < out_num ? 0 : VRING_DESC_F_WRITE) |
> +                                     (n + 1 == num ? 0 : VRING_DESC_F_NEXT));
> +        if (i == *head) {
> +            head_flags = flags;
> +        } else {
> +            descs[i].flags = flags;
> +        }
> +
> +        descs[i].addr = cpu_to_le64(sgs[n]);
> +        descs[i].id = id;
> +        if (n < out_num) {
> +            descs[i].len = cpu_to_le32(out_sg[n].iov_len);
> +        } else {
> +            descs[i].len = cpu_to_le32(in_sg[n - out_num].iov_len);
> +        }
> +
> +        curr = cpu_to_le16(svq->desc_next[curr]);
> +
> +        if (++i >= svq->vring_packed.vring.num) {
> +            i = 0;
> +            svq->vring_packed.avail_used_flags ^=
> +                    1 << VRING_PACKED_DESC_F_AVAIL |
> +                    1 << VRING_PACKED_DESC_F_USED;
> +        }
> +    }
> +
> +    if (i <= *head) {
> +        svq->vring_packed.avail_wrap_counter ^= 1;
> +    }
> +
> +    svq->vring_packed.next_avail_idx = i;
> +    svq->free_head = curr;
> +
> +    /*
> +     * A driver MUST NOT make the first descriptor in the list
> +     * available before all subsequent descriptors comprising
> +     * the list are made available.
> +     */
> +    smp_wmb();
> +    svq->vring_packed.vring.desc[*head].flags = head_flags;
> +
> +    return true;
> +}
> +
>  static void vhost_svq_kick(VhostShadowVirtqueue *svq)
>  {
>      bool needs_kick;
> @@ -258,7 +343,13 @@ int vhost_svq_add(VhostShadowVirtqueue *svq, const struct iovec *out_sg,
>          return -ENOSPC;
>      }
>
> -    ok = vhost_svq_add_split(svq, out_sg, out_num, in_sg, in_num, &qemu_head);
> +    if (virtio_vdev_has_feature(svq->vdev, VIRTIO_F_RING_PACKED)) {
> +        ok = vhost_svq_add_packed(svq, out_sg, out_num,
> +                                  in_sg, in_num, &qemu_head);
> +    } else {
> +        ok = vhost_svq_add_split(svq, out_sg, out_num,
> +                                 in_sg, in_num, &qemu_head);
> +    }
>      if (unlikely(!ok)) {
>          return -EINVAL;
>      }
> --
> 2.45.2
>

[1] https://www.qemu.org/docs/master/devel/style.html#declarations

Hi,

On Friday, July 26, 2024 7:18:28 PM GMT+5:30 Eugenio Perez Martin wrote:
> On Fri, Jul 26, 2024 at 11:58 AM Sahil Siddiq <icegambit91@gmail.com> wrote:
> > This is the first patch in a series to add support for packed
> > virtqueues in vhost_shadow_virtqueue. This patch implements the
> > insertion of available buffers in the descriptor area. It takes
> > into account descriptor chains, but does not consider indirect
> > descriptors.
> > 
> > Signed-off-by: Sahil Siddiq <sahilcdq@proton.me>
> > ---
> > Changes v1 -> v2:
> > * Split commit from RFC v1 into two commits.
> > * vhost-shadow-virtqueue.c
> > 
> >   (vhost_svq_add_packed):
> >   - Merge with "vhost_svq_vring_write_descs_packed()"
> >   - Remove "num == 0" check
> >  
> >  hw/virtio/vhost-shadow-virtqueue.c | 93 +++++++++++++++++++++++++++++-
> >  1 file changed, 92 insertions(+), 1 deletion(-)
> > 
> > diff --git a/hw/virtio/vhost-shadow-virtqueue.c
> > b/hw/virtio/vhost-shadow-virtqueue.c index fc5f408f77..c7b7e0c477 100644
> > --- a/hw/virtio/vhost-shadow-virtqueue.c
> > +++ b/hw/virtio/vhost-shadow-virtqueue.c
> > @@ -217,6 +217,91 @@ static bool vhost_svq_add_split(VhostShadowVirtqueue *svq, 
> >      return true;
> >  
> >  }
> > 
> > +static bool vhost_svq_add_packed(VhostShadowVirtqueue *svq,
> > +                                const struct iovec *out_sg, size_t out_num,
> > +                                const struct iovec *in_sg, size_t in_num,
> > +                                unsigned *head)
> > +{
> > +    bool ok;
> > +    uint16_t head_flags = 0;
> > +    g_autofree hwaddr *sgs = g_new(hwaddr, out_num + in_num);
> > +
> > +    *head = svq->vring_packed.next_avail_idx;
> > +
> > +    /* We need some descriptors here */
> > +    if (unlikely(!out_num && !in_num)) {
> > +        qemu_log_mask(LOG_GUEST_ERROR,
> > +                      "Guest provided element with no descriptors");
> > +        return false;
> > +    }
> > +
> > +    uint16_t id, curr, i;
> > +    unsigned n;
> > +    struct vring_packed_desc *descs = svq->vring_packed.vring.desc;
> > +
> > +    i = *head;
> > +    id = svq->free_head;
> > +    curr = id;
> > +
> > +    size_t num = out_num + in_num;
> > +
> > +    ok = vhost_svq_translate_addr(svq, sgs, out_sg, out_num);
> > +    if (unlikely(!ok)) {
> > +        return false;
> > +    }
> > +
> > +    ok = vhost_svq_translate_addr(svq, sgs + out_num, in_sg, in_num);
> > +    if (unlikely(!ok)) {
> > +        return false;
> > +    }
> > +
> 
> (sorry I missed this from the RFC v1) I think all of the above should
> be in the caller, isn't it? It is duplicated with split.

I don't think this will be straightforward. While they perform the same logical
step in both cases, their implementation is a little different. For example, the
"sgs" pointer is created a little differently in both cases. The parameters to
"vhost_svq_translate_addr" is also a little different. I think if they are moved to
the caller, they will be in both "svq->is_packed" branches (in "vhost_svq_add").

> Also, declarations should be at the beginning of blocks per QEMU
> coding style [1].

Sorry, I missed this. I'll rectify this.

Thanks,
Sahil

On Sun, Jul 28, 2024 at 7:37 PM Sahil <icegambit91@gmail.com> wrote:
>
> Hi,
>
> On Friday, July 26, 2024 7:18:28 PM GMT+5:30 Eugenio Perez Martin wrote:
> > On Fri, Jul 26, 2024 at 11:58 AM Sahil Siddiq <icegambit91@gmail.com> wrote:
> > > This is the first patch in a series to add support for packed
> > > virtqueues in vhost_shadow_virtqueue. This patch implements the
> > > insertion of available buffers in the descriptor area. It takes
> > > into account descriptor chains, but does not consider indirect
> > > descriptors.
> > >
> > > Signed-off-by: Sahil Siddiq <sahilcdq@proton.me>
> > > ---
> > > Changes v1 -> v2:
> > > * Split commit from RFC v1 into two commits.
> > > * vhost-shadow-virtqueue.c
> > >
> > >   (vhost_svq_add_packed):
> > >   - Merge with "vhost_svq_vring_write_descs_packed()"
> > >   - Remove "num == 0" check
> > >
> > >  hw/virtio/vhost-shadow-virtqueue.c | 93 +++++++++++++++++++++++++++++-
> > >  1 file changed, 92 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/hw/virtio/vhost-shadow-virtqueue.c
> > > b/hw/virtio/vhost-shadow-virtqueue.c index fc5f408f77..c7b7e0c477 100644
> > > --- a/hw/virtio/vhost-shadow-virtqueue.c
> > > +++ b/hw/virtio/vhost-shadow-virtqueue.c
> > > @@ -217,6 +217,91 @@ static bool vhost_svq_add_split(VhostShadowVirtqueue *svq,
> > >      return true;
> > >
> > >  }
> > >
> > > +static bool vhost_svq_add_packed(VhostShadowVirtqueue *svq,
> > > +                                const struct iovec *out_sg, size_t out_num,
> > > +                                const struct iovec *in_sg, size_t in_num,
> > > +                                unsigned *head)
> > > +{
> > > +    bool ok;
> > > +    uint16_t head_flags = 0;
> > > +    g_autofree hwaddr *sgs = g_new(hwaddr, out_num + in_num);
> > > +
> > > +    *head = svq->vring_packed.next_avail_idx;
> > > +
> > > +    /* We need some descriptors here */
> > > +    if (unlikely(!out_num && !in_num)) {
> > > +        qemu_log_mask(LOG_GUEST_ERROR,
> > > +                      "Guest provided element with no descriptors");
> > > +        return false;
> > > +    }
> > > +
> > > +    uint16_t id, curr, i;
> > > +    unsigned n;
> > > +    struct vring_packed_desc *descs = svq->vring_packed.vring.desc;
> > > +
> > > +    i = *head;
> > > +    id = svq->free_head;
> > > +    curr = id;
> > > +
> > > +    size_t num = out_num + in_num;
> > > +
> > > +    ok = vhost_svq_translate_addr(svq, sgs, out_sg, out_num);
> > > +    if (unlikely(!ok)) {
> > > +        return false;
> > > +    }
> > > +
> > > +    ok = vhost_svq_translate_addr(svq, sgs + out_num, in_sg, in_num);
> > > +    if (unlikely(!ok)) {
> > > +        return false;
> > > +    }
> > > +
> >
> > (sorry I missed this from the RFC v1) I think all of the above should
> > be in the caller, isn't it? It is duplicated with split.
>
> I don't think this will be straightforward. While they perform the same logical
> step in both cases, their implementation is a little different. For example, the
> "sgs" pointer is created a little differently in both cases.

Do you mean because MAX() vs in_num+out_num? It is ok to convert both
to the latter.

> The parameters to
> "vhost_svq_translate_addr" is also a little different. I think if they are moved to
> the caller, they will be in both "svq->is_packed" branches (in "vhost_svq_add").
>

I don't see any difference apart from calling it with in and out sgs
separately or calling it for all of the array, am I missing something?

> > Also, declarations should be at the beginning of blocks per QEMU
> > coding style [1].
>
> Sorry, I missed this. I'll rectify this.
>

No worries!

You can run scripts/checkpatch.pl in QEMU for the next series, it
should catch many of these small issues.

Thanks!

Hi,

On Monday, July 29, 2024 1:51:27 PM GMT+5:30 Eugenio Perez Martin wrote:
> On Sun, Jul 28, 2024 at 7:37 PM Sahil <icegambit91@gmail.com> wrote:
> > [...]
> > > > +static bool vhost_svq_add_packed(VhostShadowVirtqueue *svq,
> > > > +                                const struct iovec *out_sg, size_t out_num,
> > > > +                                const struct iovec *in_sg, size_t in_num,
> > > > +                                unsigned *head)
> > > > +{
> > > > +    bool ok;
> > > > +    uint16_t head_flags = 0;
> > > > +    g_autofree hwaddr *sgs = g_new(hwaddr, out_num + in_num);
> > > > +
> > > > +    *head = svq->vring_packed.next_avail_idx;
> > > > +
> > > > +    /* We need some descriptors here */
> > > > +    if (unlikely(!out_num && !in_num)) {
> > > > +        qemu_log_mask(LOG_GUEST_ERROR,
> > > > +                      "Guest provided element with no descriptors");
> > > > +        return false;
> > > > +    }
> > > > +
> > > > +    uint16_t id, curr, i;
> > > > +    unsigned n;
> > > > +    struct vring_packed_desc *descs = svq->vring_packed.vring.desc;
> > > > +
> > > > +    i = *head;
> > > > +    id = svq->free_head;
> > > > +    curr = id;
> > > > +
> > > > +    size_t num = out_num + in_num;
> > > > +
> > > > +    ok = vhost_svq_translate_addr(svq, sgs, out_sg, out_num);
> > > > +    if (unlikely(!ok)) {
> > > > +        return false;
> > > > +    }
> > > > +
> > > > +    ok = vhost_svq_translate_addr(svq, sgs + out_num, in_sg, in_num);
> > > > +    if (unlikely(!ok)) {
> > > > +        return false;
> > > > +    }
> > > > +
> > > 
> > > (sorry I missed this from the RFC v1) I think all of the above should
> > > be in the caller, isn't it? It is duplicated with split.
> > 
> > I don't think this will be straightforward. While they perform the same
> > logical step in both cases, their implementation is a little different.
> > For example, the "sgs" pointer is created a little differently in both
> > cases.
> 
> Do you mean because MAX() vs in_num+out_num? It is ok to convert both
> to the latter.
> 
> > The parameters to
> > "vhost_svq_translate_addr" is also a little different. I think if they are
> > moved to the caller, they will be in both "svq->is_packed" branches (in
> > "vhost_svq_add").
> I don't see any difference apart from calling it with in and out sgs
> separately or calling it for all of the array, am I missing something?
> 

I tried refactoring this and have sent a new patch series. Please let me
know if I have missed something.

Thanks,
Sahil