linux-kernel - Re: [PATCH RFC v1 0/2] iommu&pci: Disable ATS during FLR resets

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Message-ID: <20250610234329.GN543171@nvidia.com>
Date: Tue, 10 Jun 2025 20:43:29 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: Robin Murphy <robin.murphy@....com>, joro@...tes.org, will@...nel.org,
	bhelgaas@...gle.com, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	patches@...ts.linux.dev, pjaroszynski@...dia.com, vsethi@...dia.com
Subject: Re: [PATCH RFC v1 0/2] iommu&pci: Disable ATS during FLR resets

On Tue, Jun 10, 2025 at 01:36:45PM -0700, Nicolin Chen wrote:
> > I don't view this a problem for FLR, we can hold a mutex for a long
> > time. It principally delays domain changes which are kind of nonsense
> > to be doing concurrently with FLR in the first place..
> > 
> > However, for suspend, we probably want to leave a marker in the group
> 
> IIUIC, the thing for suspend/resume is that it would result in a
> long hold of the mutex, which can be a problem?

Yes, it would be a confusing mess to do that..

> > that the group is force-blocked and all domain attach/detach logic
> > will only update the group tracking structures and not call into the
> > iommu driver. When the resume happens the core will set the current
> > group domain list to the iommu driver. No need for a long lived lock
> > this way.
> 
> Yea, what we don't want is driver re-enabling ATS. So, bypassing
> it at the core level should work. Then, iommu_dev_reset_prepare
> and iommu_dev_reset_done will only mutex the flag.

If it is easy it seems worth including.

Jason