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

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
>

On Mon, May 15, 2023 at 01:41:12PM -0700, Shannon Nelson
wrote:
>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.
IIUC before this patch VHOST_GET_VRING_BASE and VHOST_SET_VRING_BASE
never worked with packed virtqueue, since we were only handling
last_avail_idx. Now we are supporting packed virtqueue, handling
in vhost_vring_state.num both last_avail_idx and last_used_idx (with
wrap counters).

For example for VHOST_GET_VRING_BASE where is documented that the first
15 bits are last_avail_idx, the 16th the avail_wrap_counter, and the
others are last_used_idx and used_wrap_counter?

Maybe I missed something, but since this is UAPI, IMHO we should
document the parameters of ioctls at least in
include/uapi/linux/vhost.h.

Thanks,
Stefano