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Date: Thu, 7 Nov 2024 09:41:17 +0100
From: Christoph Hellwig <hch@lst.de>
To: Yunsheng Lin <linyunsheng@huawei.com>
Cc: Jesper Dangaard Brouer <hawk@kernel.org>,
	Toke =?iso-8859-1?Q?H=F8iland-J=F8rgensen?= <toke@redhat.com>,
	davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com,
	zhangkun09@huawei.com, fanghaiqing@huawei.com,
	liuyonglong@huawei.com, Robin Murphy <robin.murphy@arm.com>,
	Alexander Duyck <alexander.duyck@gmail.com>,
	IOMMU <iommu@lists.linux.dev>,
	Andrew Morton <akpm@linux-foundation.org>,
	Eric Dumazet <edumazet@google.com>,
	Ilias Apalodimas <ilias.apalodimas@linaro.org>, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
	kernel-team <kernel-team@cloudflare.com>,
	Christoph Hellwig <hch@lst.de>, m.szyprowski@samsung.com
Subject: Re: [PATCH net-next v3 3/3] page_pool: fix IOMMU crash when driver
 has already unbound
Message-ID: <20241107084117.GA9712@lst.de>
References: <87r084e8lc.fsf@toke.dk> <cf1911c5-622f-484c-9ee5-11e1ac83da24@huawei.com> <878qu7c8om.fsf@toke.dk> <1eac33ae-e8e1-4437-9403-57291ba4ced6@huawei.com> <87o731by64.fsf@toke.dk> <023fdee7-dbd4-4e78-b911-a7136ff81343@huawei.com> <874j4sb60w.fsf@toke.dk> <a50250bf-fe76-4324-96d7-b3acf087a18c@huawei.com> <a6cfba96-9164-4497-b075-9359c18a5eef@kernel.org> <2f256bce-0c37-4940-9218-9545daa46169@huawei.com>
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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.