linux-kernel - Re: [PATCH net-next v3 3/3] page_pool: fix IOMMU crash when driver has already unbound

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Message-ID: <20241107084117.GA9712@lst.de>
Date: Thu, 7 Nov 2024 09:41:17 +0100
From: Christoph Hellwig <hch@....de>
To: Yunsheng Lin <linyunsheng@...wei.com>
Cc: Jesper Dangaard Brouer <hawk@...nel.org>,
	Toke Høiland-Jørgensen <toke@...hat.com>,
	davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
	zhangkun09@...wei.com, fanghaiqing@...wei.com,
	liuyonglong@...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>,
	Ilias Apalodimas <ilias.apalodimas@...aro.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	kernel-team <kernel-team@...udflare.com>,
	Christoph Hellwig <hch@....de>, m.szyprowski@...sung.com
Subject: Re: [PATCH net-next v3 3/3] page_pool: fix IOMMU crash when driver
 has already unbound

On Wed, Nov 06, 2024 at 06:56:34PM +0800, Yunsheng Lin wrote:
> > It is a very radical change that page_pool needs to keep track of *ALL* in-flight pages.
> 
> I am agreed that it is a radical change, that is why it is targetting net-next
> tree instead of net tree even when there is a Fixes tag for it.
> 
> If there is a proper and non-radical way to fix that, I would prefer the
> non-radical way too.

As Robin already correctly pointed out DMA mappings fundamentally can't
outlive the devices they were performed on.  So I don't think there will
be much hope for a non-radical fix for this design fault.