Re: [PATCH 0/2] Search the split vq desc and avail in RO areas

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 6/6/25 4:20 PM, David Marchand wrote:
> On Thu, Jun 5, 2025 at 4:55 PM Eugenio Perez Martin <eperezma@redhat.com> wrote:
>>
>> On Thu, Jun 5, 2025 at 1:50 PM David Marchand <david.marchand@redhat.com> wrote:
>>>
>>> On Thu, Jun 5, 2025 at 1:36 PM Eugenio Pérez <eperezma@redhat.com> wrote:
>>>>
>>>> QEMU's shadow virtqueue and VDUSE exposes these areas as read-only. If
>>>> we don't change it, vhost_iova_to_vva do not consider them as valid and
>>>> returns that they're not found.
>>>>
>>>> Eugenio Pérez (2):
>>>>    vhost: search the split vq desc and avail in RO areas
>>>>    vhost: search the packed vq driver area in RO areas
>>>>
>>>>   lib/vhost/vhost.c | 6 +++---
>>>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> At a quick glance, no need for two patches.
>>>
>>
>> Sure I can respin with both squashed.
>>
>>> Sorry, the implication of this issue is not clear to me.
>>> What is the impact from a user pov?
>>>
>>
>> QEMU maps the CVQ descriptors and avail vring through as read only
>> maps in the case of vDPA. But DPDK is looking for them with RW
>> permissions, so the vhost_iova_to_vva function never selects the right
>> one as valid.
>>
>> Looking for them with RO still picks the map if it is mapped as RW,
>> but the reverse is not true.
> 
> Ok, thanks.
> Well, it's better, but still hard to tell how this impacts existing
> usecases :-).
> After discussing with Maxime, I understand that the shadow CVQ just
> can't work => blocking multi queue support with vduse for example.
> This is the type of high level impact I was looking for.
> 
>> Let me know if you want me to respin the series with this comment too!
> 
> Ideally yes, but maybe Maxime can do it when applying.
> 
> 

Yes, I can rework the commit message while applying.

Thanks,
Maxime