RE: [PATCH 4/5] vfio/type1: Flush CPU caches on DMA pages in non-coherent domains

Tian, Kevin
2024-05-22T23:26:25Z

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Wednesday, May 22, 2024 8:30 PM
>
> On Wed, May 22, 2024 at 06:24:14AM +0000, Tian, Kevin wrote:
> > I'm fine to do a special check in the attach path to enable the flush
> > only for Intel GPU.
>
> We already effectively do this already by checking the domain
> capabilities. Only the Intel GPU will have a non-coherent domain.
>

I'm confused. In earlier discussions you wanted to find a way to not
publish others due to the check of non-coherent domain, e.g. some
ARM SMMU cannot force snoop.

Then you and Alex discussed the possibility of reducing pessimistic
flushes by virtualizing the PCI NOSNOOP bit.

With that in mind I was thinking whether we explicitly enable this
flush only for Intel GPU instead of checking non-coherent domain
in the attach path, since it's the only device with such requirement.

Did I misunderstand the concern here?