[PATCH slof] virtio: Fix vring allocation

[PATCH slof] virtio: Fix vring allocation

[Alexey Kardashevskiy]

The value returned by virtio_vring_size() is used to allocate memory
for vring. The used descriptor list (array of vring_used_elem) is
counted by the header - vring_used struct - is not.

This fixes virtio_vring_size() to return the correct size.
At the moment rings are quite small (256) and allocated with
4096 alignment, this is why we have not been having issues with
this so far.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
 lib/libvirtio/virtio.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/libvirtio/virtio.c b/lib/libvirtio/virtio.c
index b010796..22615c4 100644
--- a/lib/libvirtio/virtio.c
+++ b/lib/libvirtio/virtio.c
@@ -33,7 +33,8 @@
 unsigned long virtio_vring_size(unsigned int qsize)
 {
 	return VQ_ALIGN(sizeof(struct vring_desc) * qsize + 2 * (2 + qsize))
-		+ VQ_ALIGN(sizeof(struct vring_used_elem) * qsize);
+               + VQ_ALIGN(sizeof(struct vring_used) +
+                          sizeof(struct vring_used_elem) * qsize);
 }
 
 
-- 
2.0.0

Re: [PATCH slof] virtio: Fix vring allocation

[Nikunj A Dadhania]

Alexey Kardashevskiy <aik@ozlabs.ru> writes:

> The value returned by virtio_vring_size() is used to allocate memory
> for vring. The used descriptor list (array of vring_used_elem) is
> counted by the header - vring_used struct - is not.
>
> This fixes virtio_vring_size() to return the correct size.
> At the moment rings are quite small (256) and allocated with
> 4096 alignment, this is why we have not been having issues with
> this so far.
>
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
>  lib/libvirtio/virtio.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/lib/libvirtio/virtio.c b/lib/libvirtio/virtio.c
> index b010796..22615c4 100644
> --- a/lib/libvirtio/virtio.c
> +++ b/lib/libvirtio/virtio.c
> @@ -33,7 +33,8 @@
>  unsigned long virtio_vring_size(unsigned int qsize)
>  {
>  	return VQ_ALIGN(sizeof(struct vring_desc) * qsize + 2 * (2 + qsize))

While at it, lets not have the above magic numbers as well ^^^^^^^^^^

sizeof(struct vring_avail) + sizeof(uint16_t) * qsize

> -		+ VQ_ALIGN(sizeof(struct vring_used_elem) * qsize);
> +               + VQ_ALIGN(sizeof(struct vring_used) +
> +                          sizeof(struct vring_used_elem) * qsize);
>  }
>
>
> -- 
> 2.0.0

Regards
Nikunj

[PATCH slof v2] virtio: Fix vring allocation

[Alexey Kardashevskiy]

The value returned by virtio_vring_size() is used to allocate memory
for vring. The used descriptor list (array of vring_used_elem) is
counted by the header - vring_used struct - is not.

This fixes virtio_vring_size() to return the correct size.
At the moment rings are quite small (256) and allocated with
4096 alignment, this is why we have not been having issues with
this so far.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
Changes:
v2:
* remove magic numbers
---
 lib/libvirtio/virtio.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/libvirtio/virtio.c b/lib/libvirtio/virtio.c
index b010796..f9c00a6 100644
--- a/lib/libvirtio/virtio.c
+++ b/lib/libvirtio/virtio.c
@@ -32,8 +32,10 @@
  */
 unsigned long virtio_vring_size(unsigned int qsize)
 {
-	return VQ_ALIGN(sizeof(struct vring_desc) * qsize + 2 * (2 + qsize))
-		+ VQ_ALIGN(sizeof(struct vring_used_elem) * qsize);
+	return VQ_ALIGN(sizeof(struct vring_desc) * qsize +
+                        sizeof(struct vring_avail) + sizeof(uint16_t) * qsize) +
+               VQ_ALIGN(sizeof(struct vring_used) +
+                        sizeof(struct vring_used_elem) * qsize);
 }
 
 
-- 
2.0.0

Re: [PATCH slof v2] virtio: Fix vring allocation

[Nikunj A Dadhania]

Alexey Kardashevskiy <aik@ozlabs.ru> writes:

> The value returned by virtio_vring_size() is used to allocate memory
> for vring. The used descriptor list (array of vring_used_elem) is
> counted by the header - vring_used struct - is not.
>
> This fixes virtio_vring_size() to return the correct size.
> At the moment rings are quite small (256) and allocated with
> 4096 alignment, this is why we have not been having issues with
> this so far.
>
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

Reviewed-by: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>

> ---
> Changes:
> v2:
> * remove magic numbers
> ---
>  lib/libvirtio/virtio.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/lib/libvirtio/virtio.c b/lib/libvirtio/virtio.c
> index b010796..f9c00a6 100644
> --- a/lib/libvirtio/virtio.c
> +++ b/lib/libvirtio/virtio.c
> @@ -32,8 +32,10 @@
>   */
>  unsigned long virtio_vring_size(unsigned int qsize)
>  {
> -	return VQ_ALIGN(sizeof(struct vring_desc) * qsize + 2 * (2 + qsize))
> -		+ VQ_ALIGN(sizeof(struct vring_used_elem) * qsize);
> +	return VQ_ALIGN(sizeof(struct vring_desc) * qsize +
> +                        sizeof(struct vring_avail) + sizeof(uint16_t) * qsize) +
> +               VQ_ALIGN(sizeof(struct vring_used) +
> +                        sizeof(struct vring_used_elem) * qsize);
>  }
>
>
> -- 
> 2.0.0

Re: [PATCH slof v2] virtio: Fix vring allocation

[Thomas Huth]

On Fri, 13 Mar 2015 20:42:03 +1100
Alexey Kardashevskiy <aik@ozlabs.ru> wrote:

> The value returned by virtio_vring_size() is used to allocate memory
> for vring. The used descriptor list (array of vring_used_elem) is
> counted by the header - vring_used struct - is not.
> 
> This fixes virtio_vring_size() to return the correct size.
> At the moment rings are quite small (256) and allocated with
> 4096 alignment, this is why we have not been having issues with
> this so far.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
> Changes:
> v2:
> * remove magic numbers
> ---
>  lib/libvirtio/virtio.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/libvirtio/virtio.c b/lib/libvirtio/virtio.c
> index b010796..f9c00a6 100644
> --- a/lib/libvirtio/virtio.c
> +++ b/lib/libvirtio/virtio.c
> @@ -32,8 +32,10 @@
>   */
>  unsigned long virtio_vring_size(unsigned int qsize)
>  {
> -	return VQ_ALIGN(sizeof(struct vring_desc) * qsize + 2 * (2 + qsize))
> -		+ VQ_ALIGN(sizeof(struct vring_used_elem) * qsize);
> +	return VQ_ALIGN(sizeof(struct vring_desc) * qsize +
> +                        sizeof(struct vring_avail) + sizeof(uint16_t) * qsize) +
> +               VQ_ALIGN(sizeof(struct vring_used) +
> +                        sizeof(struct vring_used_elem) * qsize);
>  }

Reviewed-by: Thomas Huth <thuth@linux.vnet.ibm.com>

That should be at least ok for the current status that we support in
SLOF. I think I might have written the original version of that
function with a very old version of the virtio spec (v0.8.10), when
ther was no "used_event" event field in the struct vring_avail defined
yet.
But if SLOF ever supports VIRTIO_F_EVENT_IDX, we've got to keep in mind
to add some additional bytes here, too.

 Thomas