linux-kernel - Re: [PATCH v2] iommu/vt-d: fix system hang on reboot -f

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Message-ID: <f29818dc-a0a7-46c4-b541-1b469a6b3304@gmail.com>
Date: Thu, 27 Feb 2025 08:40:31 +0800
From: Ethan Zhao <etzhao1900@...il.com>
To: Jason Gunthorpe <jgg@...pe.ca>, Ethan Zhao <haifeng.zhao@...ux.intel.com>
Cc: Baolu Lu <baolu.lu@...ux.intel.com>, Yunhui Cui
 <cuiyunhui@...edance.com>, dwmw2@...radead.org, joro@...tes.org,
 will@...nel.org, robin.murphy@....com, iommu@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] iommu/vt-d: fix system hang on reboot -f

On 2/26/2025 9:04 PM, Jason Gunthorpe wrote:
> On Wed, Feb 26, 2025 at 01:55:28PM +0800, Ethan Zhao wrote:
>>> Provided the system does not respond to those events when this function
>>> is called, it's fine to remove the lock.
>> I agree.
> I think it is running the destruction of the iommu far too late in the
> process. IMHO it should be done after all the drivers have been
> shutdown, before the CPUs go single threaded.

Hmm... so far it is fine, the iommu_shutdown only has a little work to
do, disable the translation, the PMR disabling is just backward compatible,
was deprecated already. if we move it to one position where all CPUs are
cycling, we don't know what kind of user-land tasks left there (i.e. reboot -f
case), it would be hard to full-fill the requirement of Intel VT-d, no ongoing
transaction there on hardware when issue the translation disabling command.

Of course, once you have clear motivation to re-position it. we would like
to work on it.

Thanks,
Ethan

>
> Jason
>