Re: [RFC v8 3/5] page_pool: fix IOMMU crash when driver has already unbound

[Mina Almasry <almasrymina@google.com>]

On Tue, Feb 4, 2025 at 6:23 AM Yunsheng Lin <yunshenglin0825@gmail.com> wrote:
>
> On 1/28/2025 2:12 PM, Christoph Hellwig wrote:
> > On Mon, Jan 27, 2025 at 10:57:32AM +0800, Yunsheng Lin wrote:
> >> Note, the devmem patchset seems to make the bug harder to fix,
> >> and may make backporting harder too. As there is no actual user
> >> for the devmem and the fixing for devmem is unclear for now,
> >> this patch does not consider fixing the case for devmem yet.
> >
> > Is there another outstanding patchet?  Or do you mean the existing
> > devmem code already merged?  If that isn't actually used it should
> > be removed, but otherwise you need to fix it.
>
> The last time I checked, only the code for networking stack supporting
> the devmem had been merged.
>
> The first driver suppporting seems to be bnxt, which seems to be under
> review:
> https://lore.kernel.org/all/20241022162359.2713094-1-ap420073@gmail.com/
>
> As my understanding, this should work for the devmem too if the devmem

From a quick look at this patch, it looks like you're handling
netmem/net_iovs in the implementation, so this implementation is
indeed considering netmem. I think the paragraph in the commit message
that Christoph is responding to should be deleted, because in recent
iterations you're handling netmem.

> provide a ops to do the per-netmem dma unmapping
> It would be good that devmem people can have a look at it and see if
> this fix works for the specific page_pool mp provider.
>

We set pool->dma_map==false for memory providers that do not need
mapping/unmapping, which you are checking in
__page_pool_release_page_dma.

-- 
Thanks,
Mina