linux-kernel - Re: [PATCH 1/1] iommu/vt-d: Fix missed device TLB cache tag

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Date: Wed, 19 Jun 2024 13:46:20 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Lu Baolu <baolu.lu@...ux.intel.com>
Cc: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>,
	Kevin Tian <kevin.tian@...el.com>,
	Jacek Lawrynowicz <jacek.lawrynowicz@...ux.intel.com>,
	iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] iommu/vt-d: Fix missed device TLB cache tag

On Wed, Jun 19, 2024 at 09:53:45AM +0800, Lu Baolu wrote:
> When a domain is attached to a device, the required cache tags are
> assigned to the domain so that the related caches could be flushed
> whenever it is needed. The device TLB cache tag is created selectively 
> by checking the ats_enabled field of the device's iommu data. This
> creates an ordered dependency between attach and ATS enabling paths.
> 
> The device TLB cache tag will not be created if device's ATS is enabled
> after the domain attachment. This causes some devices, for example
> intel_vpu, to malfunction.

What? How is this even possible?

ATS is controlled exclusively by the iommu driver, how can it be
changed without the driver knowing??

Jason