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

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Message-ID: <c4b8f494-1928-4cf6-afe2-61ab1ac7e641@gmail.com>
Date: Tue, 4 Feb 2025 22:23:43 +0800
From: Yunsheng Lin <yunshenglin0825@...il.com>
To: Christoph Hellwig <hch@...radead.org>,
 Yunsheng Lin <linyunsheng@...wei.com>
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
 zhangkun09@...wei.com, liuyonglong@...wei.com, fanghaiqing@...wei.com,
 Robin Murphy <robin.murphy@....com>,
 Alexander Duyck <alexander.duyck@...il.com>, IOMMU <iommu@...ts.linux.dev>,
 Andrew Morton <akpm@...ux-foundation.org>, Eric Dumazet
 <edumazet@...gle.com>, Simon Horman <horms@...nel.org>,
 Jesper Dangaard Brouer <hawk@...nel.org>,
 Ilias Apalodimas <ilias.apalodimas@...aro.org>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [RFC v8 3/5] page_pool: fix IOMMU crash when driver has already
 unbound

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
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.