Subject: Re: [PATCH net-next v2 4/5] page_pool: disable sync for cpu for dmabuf memory provider

From: Stanislav Fomichev <[email-masked]>
Date: Fri, 8 Nov 2024 07:58:22 -0800

On 11/08, Jason Gunthorpe wrote:
> On Thu, Nov 07, 2024 at 09:23:08PM +0000, Mina Almasry wrote:
> > dmabuf dma-addresses should not be dma_sync'd for CPU/device. Typically
> > its the driver responsibility to dma_sync for CPU, but the driver should
> > not dma_sync for CPU if the netmem is actually coming from a dmabuf
> > memory provider.
> 
> This is not completely true, it is not *all* dmabuf, just the parts of
> the dmabuf that are actually MMIO.
> 
> If you do this you may want to block accepting dmabufs that have CPU
> pages inside them.

We still want udmabufs to work, so probably need some new helper to test
whether a particular netmem is backed by the cpu memory?