This is suggested by Michael S. Tsirkin according to [1] and the goal
is to apply smp_rmb() inside vhost_get_avail_idx() if needed. With it,
the caller of the function needn't to worry about memory barriers. Since
we're here, other cleanups are also applied.

[1] https://lore.kernel.org/virtualization/20240327075940-mutt-send-email-mst@kernel.org/

PATCH[1] drops the local variable @last_avail_idx since it's equivalent
         to vq->last_avail_idx
PATCH[2] improves vhost_get_avail_idx() so that smp_rmb() is applied if
         needed. Besides, the sanity checks on the retrieved available
         queue index are also squeezed to vhost_get_avail_idx()
PATCH[3] improves vhost_get_avail_head(), similar to what we're doing
         for vhost_get_avail_idx(), so that the relevant sanity checks
         on the head are squeezed to vhost_get_avail_head()
PATCH[4] Reformat vhost_{get, put}_user() by using tab instead of space
         as the terminator for each line

Gavin Shan (4):
  vhost: Drop variable last_avail_idx in vhost_get_vq_desc()
  vhost: Improve vhost_get_avail_idx() with smp_rmb()
  vhost: Improve vhost_get_avail_head()
  vhost: Reformat vhost_{get, put}_user()

 drivers/vhost/vhost.c | 199 +++++++++++++++++++-----------------------
 1 file changed, 88 insertions(+), 111 deletions(-)

-- 
2.44.0

On Tue, Apr 23, 2024 at 01:24:03PM +1000, Gavin Shan wrote:
> This is suggested by Michael S. Tsirkin according to [1] and the goal
> is to apply smp_rmb() inside vhost_get_avail_idx() if needed. With it,
> the caller of the function needn't to worry about memory barriers. Since
> we're here, other cleanups are also applied.


Gavin I suggested another approach.
1. Start with the patch I sent (vhost: order avail ring reads after
   index updates) just do a diff against latest.
   simplify error handling a bit.
2. Do any other cleanups on top.

> [1] https://lore.kernel.org/virtualization/20240327075940-mutt-send-email-mst@kernel.org/
> 
> PATCH[1] drops the local variable @last_avail_idx since it's equivalent
>          to vq->last_avail_idx
> PATCH[2] improves vhost_get_avail_idx() so that smp_rmb() is applied if
>          needed. Besides, the sanity checks on the retrieved available
>          queue index are also squeezed to vhost_get_avail_idx()
> PATCH[3] improves vhost_get_avail_head(), similar to what we're doing
>          for vhost_get_avail_idx(), so that the relevant sanity checks
>          on the head are squeezed to vhost_get_avail_head()
> PATCH[4] Reformat vhost_{get, put}_user() by using tab instead of space
>          as the terminator for each line
> 
> Gavin Shan (4):
>   vhost: Drop variable last_avail_idx in vhost_get_vq_desc()
>   vhost: Improve vhost_get_avail_idx() with smp_rmb()
>   vhost: Improve vhost_get_avail_head()
>   vhost: Reformat vhost_{get, put}_user()
> 
>  drivers/vhost/vhost.c | 199 +++++++++++++++++++-----------------------
>  1 file changed, 88 insertions(+), 111 deletions(-)
> 
> -- 
> 2.44.0

On 4/29/24 17:02, Michael S. Tsirkin wrote:
> On Tue, Apr 23, 2024 at 01:24:03PM +1000, Gavin Shan wrote:
>> This is suggested by Michael S. Tsirkin according to [1] and the goal
>> is to apply smp_rmb() inside vhost_get_avail_idx() if needed. With it,
>> the caller of the function needn't to worry about memory barriers. Since
>> we're here, other cleanups are also applied.
> 
> 
> Gavin I suggested another approach.
> 1. Start with the patch I sent (vhost: order avail ring reads after
>     index updates) just do a diff against latest.
>     simplify error handling a bit.
> 2. Do any other cleanups on top.
> 

My apologies, Michael. I didn't see your patch until now [1]

   [1] https://lore.kernel.org/virtualization/20240327155750-mutt-send-email-mst@kernel.org/

v2 was sent with your changes integrated and other cleanup are applied on
top of it. Please take a look when you getting a chance.

   v2: https://lore.kernel.org/virtualization/20240429101400.617007-1-gshan@redhat.com/T/#t

Thanks,
Gavin