Virtualization - May 2023 - [PATCH v2 2/3] vhost: support PACKED when setting-getting vring_base

On Mon, Apr 24, 2023 at 03:50:30PM -0700, Shannon Nelson via Virtualization
wrote:
>Use the right structs for PACKED or split vqs when setting and
>getting the vring base.
>
>Signed-off-by: Shannon Nelson <shannon.nelson at amd.com>
>---
> drivers/vhost/vhost.c | 18 +++++++++++++-----
> drivers/vhost/vhost.h |  8 ++++++--
> 2 files changed, 19 insertions(+), 7 deletions(-)
>
>diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>index f11bdbe4c2c5..f64efda48f21 100644
>--- a/drivers/vhost/vhost.c
>+++ b/drivers/vhost/vhost.c
>@@ -1633,17 +1633,25 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned
int ioctl, void __user *arg
> 			r = -EFAULT;
> 			break;
> 		}
>-		if (s.num > 0xffff) {
>-			r = -EINVAL;
>-			break;
>+		if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED)) {
>+			vq->last_avail_idx = s.num & 0xffff;
>+			vq->last_used_idx = (s.num >> 16) & 0xffff;
>+		} else {
>+			if (s.num > 0xffff) {
>+				r = -EINVAL;
>+				break;
>+			}
>+			vq->last_avail_idx = s.num;
> 		}
>-		vq->last_avail_idx = s.num;
> 		/* Forget the cached index value. */
> 		vq->avail_idx = vq->last_avail_idx;
> 		break;
> 	case VHOST_GET_VRING_BASE:
> 		s.index = idx;
>-		s.num = vq->last_avail_idx;
>+		if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED))
>+			s.num = (u32)vq->last_avail_idx | ((u32)vq->last_used_idx <<
16);
>+		else
>+			s.num = vq->last_avail_idx;
The changes LGTM, but since we are changing the UAPI, should we
update the documentation of VHOST_SET_VRING_BASE and
VHOST_GET_VRING_BASE in include/uapi/linux/vhost.h?

Thanks,
Stefano

On 5/9/23 1:46 AM, Stefano Garzarella wrote:
> On Mon, Apr 24, 2023 at 03:50:30PM -0700, Shannon Nelson via 
> Virtualization wrote:
>> Use the right structs for PACKED or split vqs when setting and
>> getting the vring base.
>>
>> Signed-off-by: Shannon Nelson <shannon.nelson at amd.com>
>> ---
>> drivers/vhost/vhost.c | 18 +++++++++++++-----
>> drivers/vhost/vhost.h |? 8 ++++++--
>> 2 files changed, 19 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>> index f11bdbe4c2c5..f64efda48f21 100644
>> --- a/drivers/vhost/vhost.c
>> +++ b/drivers/vhost/vhost.c
>> @@ -1633,17 +1633,25 @@ long vhost_vring_ioctl(struct vhost_dev *d, 
>> unsigned int ioctl, void __user *arg
>> ????????????????????? r = -EFAULT;
>> ????????????????????? break;
>> ????????????? }
>> -????????????? if (s.num > 0xffff) {
>> -????????????????????? r = -EINVAL;
>> -????????????????????? break;
>> +????????????? if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED)) {
>> +????????????????????? vq->last_avail_idx = s.num & 0xffff;
>> +????????????????????? vq->last_used_idx = (s.num >> 16) &
0xffff;
>> +????????????? } else {
>> +????????????????????? if (s.num > 0xffff) {
>> +????????????????????????????? r = -EINVAL;
>> +????????????????????????????? break;
>> +????????????????????? }
>> +????????????????????? vq->last_avail_idx = s.num;
>> ????????????? }
>> -????????????? vq->last_avail_idx = s.num;
>> ????????????? /* Forget the cached index value. */
>> ????????????? vq->avail_idx = vq->last_avail_idx;
>> ????????????? break;
>> ????? case VHOST_GET_VRING_BASE:
>> ????????????? s.index = idx;
>> -????????????? s.num = vq->last_avail_idx;
>> +????????????? if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED))
>> +????????????????????? s.num = (u32)vq->last_avail_idx | 
>> ((u32)vq->last_used_idx << 16);
>> +????????????? else
>> +????????????????????? s.num = vq->last_avail_idx;
> 
> The changes LGTM, but since we are changing the UAPI, should we
> update the documentation of VHOST_SET_VRING_BASE and
> VHOST_GET_VRING_BASE in include/uapi/linux/vhost.h?
Correct me if I'm wrong, but I don't think we're changing anything
in
the UAPI here, just fixing code to work correctly with what is already 
happening.

sln

> 
> Thanks,
> Stefano
>