Virtualization - Aug 2022 - [PATCH 2/2] vDPA: conditionally read fields in virtio-net dev

On Wed, Aug 17, 2022 at 05:43:22PM +0800, Zhu, Lingshan
wrote:
> 
> 
> On 8/17/2022 5:39 PM, Michael S. Tsirkin wrote:
> > On Wed, Aug 17, 2022 at 05:13:59PM +0800, Zhu, Lingshan wrote:
> > > 
> > > On 8/17/2022 4:55 PM, Michael S. Tsirkin wrote:
> > > > On Wed, Aug 17, 2022 at 10:14:26AM +0800, Zhu, Lingshan
wrote:
> > > > > Yes it is a little messy, and we can not check
_F_VERSION_1 because of
> > > > > transitional devices, so maybe this is the best we can
do for now
> > > > I think vhost generally needs an API to declare config space
endian-ness
> > > > to kernel. vdpa can reuse that too then.
> > > Yes, I remember you have mentioned some IOCTL to set the
endian-ness,
> > > for vDPA, I think only the vendor driver knows the endian,
> > > so we may need a new function vdpa_ops->get_endian().
> > > In the last thread, we say maybe it's better to add a comment
for now.
> > > But if you think we should add a vdpa_ops->get_endian(), I can
work
> > > on it for sure!
> > > 
> > > Thanks
> > > Zhu Lingshan
> > I think QEMU has to set endian-ness. No one else knows.
> Yes, for SW based vhost it is true. But for HW vDPA, only
> the device & driver knows the endian, I think we can not
> "set" a hardware's endian.
QEMU knows the guest endian-ness and it knows that
device is accessed through the legacy interface.
It can accordingly send endian-ness to the kernel and
kernel can propagate it to the driver.
> So if you think we should add a vdpa_ops->get_endian(),
> I will drop these comments in the next version of
> series, and work on a new patch for get_endian().
> 
> Thanks,
> Zhu Lingshan
Guests don't get endian-ness from devices so this seems pointless.

-- 
MST

? 2022/8/17 18:37, Michael S. Tsirkin ??:
> On Wed, Aug 17, 2022 at 05:43:22PM +0800, Zhu, Lingshan wrote:
>>
>> On 8/17/2022 5:39 PM, Michael S. Tsirkin wrote:
>>> On Wed, Aug 17, 2022 at 05:13:59PM +0800, Zhu, Lingshan wrote:
>>>> On 8/17/2022 4:55 PM, Michael S. Tsirkin wrote:
>>>>> On Wed, Aug 17, 2022 at 10:14:26AM +0800, Zhu, Lingshan
wrote:
>>>>>> Yes it is a little messy, and we can not check
_F_VERSION_1 because of
>>>>>> transitional devices, so maybe this is the best we can
do for now
>>>>> I think vhost generally needs an API to declare config
space endian-ness
>>>>> to kernel. vdpa can reuse that too then.
>>>> Yes, I remember you have mentioned some IOCTL to set the
endian-ness,
>>>> for vDPA, I think only the vendor driver knows the endian,
>>>> so we may need a new function vdpa_ops->get_endian().
>>>> In the last thread, we say maybe it's better to add a
comment for now.
>>>> But if you think we should add a vdpa_ops->get_endian(), I
can work
>>>> on it for sure!
>>>>
>>>> Thanks
>>>> Zhu Lingshan
>>> I think QEMU has to set endian-ness. No one else knows.
>> Yes, for SW based vhost it is true. But for HW vDPA, only
>> the device & driver knows the endian, I think we can not
>> "set" a hardware's endian.
> QEMU knows the guest endian-ness and it knows that
> device is accessed through the legacy interface.
> It can accordingly send endian-ness to the kernel and
> kernel can propagate it to the driver.

I wonder if we can simply force LE and then Qemu can do the endian 
conversion?

Thanks

>
>> So if you think we should add a vdpa_ops->get_endian(),
>> I will drop these comments in the next version of
>> series, and work on a new patch for get_endian().
>>
>> Thanks,
>> Zhu Lingshan
> Guests don't get endian-ness from devices so this seems pointless.
>