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

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Message-ID: <CAC_iWjLmWtN51eLnnuPtL5vzTBQF2v43zyoV1+AZqUmuSD1DGg@mail.gmail.com>
Date: Tue, 24 Sep 2024 09:27:07 +0300
From: Ilias Apalodimas <ilias.apalodimas@...aro.org>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Yunsheng Lin <linyunsheng@...wei.com>, Jesper Dangaard Brouer <hawk@...nel.org>, davem@...emloft.net, 
	kuba@...nel.org, pabeni@...hat.com, 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>, 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
Subject: Re: [PATCH net 2/2] page_pool: fix IOMMU crash when driver has
 already unbound

Hi Jason,

On Mon, 23 Sept 2024 at 20:52, Jason Gunthorpe <jgg@...pe.ca> wrote:
>
> On Fri, Sep 20, 2024 at 02:14:02PM +0800, Yunsheng Lin wrote:
>
> > I am not sure what dose the API that allows netdev to "give" struct device
> > to page_pool look like or how to implement the API yet, but the obvious way
> > to stall the calling of device_del() is to wait for the inflight
> > page to
>
> It is not device_del() you need to stall, but the remove() function of
> the device driver.
>
> Once all drivers have been unbound the DMA API can be reconfigured and
> all existing DMA mappings must be concluded before this happens,
> otherwise there will be problems.
>
> So, stalling something like unregister_netdevice() would be a better
> target - though stalling forever on driver unbind would not be
> acceptable.

TBH, I have doubts that even stalling it for small amounts of time is
going to disrupt userspace and people are going to yell at us.
I am gonna repeat myself here, but I think keeping a list of the
inflight SKBs that we need to unmap when the interface goes down, is
the most complex, but less disruptive solution

Thanks
/Ilias
>
> Jason