linux-kernel - Re: [PATCH net v2 2/2] page_pool: fix IOMMU crash when driver has already unbound

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Message-ID: <4316fa2d-8dd8-44f2-b211-4b2ef3200d75@redhat.com>
Date: Wed, 2 Oct 2024 09:37:54 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Yunsheng Lin <yunshenglin0825@...il.com>,
 Yunsheng Lin <linyunsheng@...wei.com>,
 Ilias Apalodimas <ilias.apalodimas@...aro.org>
Cc: liuyonglong@...wei.com, fanghaiqing@...wei.com, zhangkun09@...wei.com,
 Robin Murphy <robin.murphy@....com>,
 Alexander Duyck <alexander.duyck@...il.com>, IOMMU <iommu@...ts.linux.dev>,
 Wei Fang <wei.fang@....com>, Shenwei Wang <shenwei.wang@....com>,
 Clark Wang <xiaoning.wang@....com>, Eric Dumazet <edumazet@...gle.com>,
 Tony Nguyen <anthony.l.nguyen@...el.com>,
 Przemek Kitszel <przemyslaw.kitszel@...el.com>,
 Alexander Lobakin <aleksander.lobakin@...el.com>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Jesper Dangaard Brouer <hawk@...nel.org>,
 John Fastabend <john.fastabend@...il.com>, Saeed Mahameed
 <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>,
 Tariq Toukan <tariqt@...dia.com>, Felix Fietkau <nbd@....name>,
 Lorenzo Bianconi <lorenzo@...nel.org>, Ryder Lee <ryder.lee@...iatek.com>,
 Shayne Chen <shayne.chen@...iatek.com>, Sean Wang <sean.wang@...iatek.com>,
 Kalle Valo <kvalo@...nel.org>, Matthias Brugger <matthias.bgg@...il.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 Andrew Morton <akpm@...ux-foundation.org>, imx@...ts.linux.dev,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 intel-wired-lan@...ts.osuosl.org, bpf@...r.kernel.org,
 linux-rdma@...r.kernel.org, linux-wireless@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org,
 linux-mm@...ck.org, davem@...emloft.net, kuba@...nel.org
Subject: Re: [PATCH net v2 2/2] page_pool: fix IOMMU crash when driver has
 already unbound

Hi,

On 10/2/24 04:34, Yunsheng Lin wrote:
> On 10/1/2024 9:32 PM, Paolo Abeni wrote:
>> Is the problem only tied to VFs drivers? It's a pity all the page_pool
>> users will have to pay a bill for it...
> 
> I am afraid it is not only tied to VFs drivers, as:
> attempting DMA unmaps after the driver has already unbound may leak
> resources or at worst corrupt memory.
> 
> Unloading PFs driver might cause the above problems too, I guess the
> probability of crashing is low for the PF as PF can not be disable
> unless it can be hot-unplug'ed, but the probability of leaking resources
> behind the dma mapping might be similar.

Out of sheer ignorance, why/how the refcount acquired by the page pool 
on the device does not prevent unloading?

I fear the performance impact could be very high: AFICS, if the item 
array become fragmented, insertion will take linar time, with the quite 
large item_count/pool size. If so, it looks like a no-go.

I fear we should consider blocking the device removal until all the 
pages are returned/unmapped ?!? (I hope that could be easier/faster)

/P