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

[Shannon Nelson via Virtualization <virtualization@lists.linux-foundation.org>]

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@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
> 
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