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

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Message-ID: <20250227203855.GI5011@ziepe.ca>
Date: Thu, 27 Feb 2025 16:38:55 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Ethan Zhao <etzhao1900@...il.com>
Cc: Ethan Zhao <haifeng.zhao@...ux.intel.com>,
	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 Thu, Feb 27, 2025 at 08:40:31AM +0800, Ethan Zhao wrote:
> 
> 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.

There is no guarentee device dma is halted anyhow at this point either.

Jason