linux-kernel - Re: [PATCH REGRESSION] iommu: Only allocate FQ domains for IOMMUs that support them

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Date:   Sun, 24 Sep 2023 09:49:31 +0200
From:   "Linux regression tracking #adding (Thorsten Leemhuis)" 
        <regressions@...mhuis.info>
To:     Hector Martin <marcan@...can.st>, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jerry Snitselaar <jsnitsel@...hat.com>
Cc:     Joerg Roedel <jroedel@...e.de>, Neal Gompa <neal@...pa.dev>,
        "Justin M. Forbes" <jforbes@...oraproject.org>,
        iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
        asahi@...ts.linux.dev, stable@...r.kernel.org,
        regressions@...ts.linux.dev
Subject: Re: [PATCH REGRESSION] iommu: Only allocate FQ domains for IOMMUs
 that support them

[TLDR: I'm adding this report to the list of tracked Linux kernel
regressions; the text you find below is based on a few templates
paragraphs you might have encountered already in similar form.
See link in footer if these mails annoy you.]

On 22.09.23 15:40, Hector Martin wrote:
> Commit a4fdd9762272 ("iommu: Use flush queue capability") hid the
> IOMMU_DOMAIN_DMA_FQ domain type from domain allocation. A check was
> introduced in iommu_dma_init_domain() to fall back if not supported, but
> this check runs too late: by that point, devices have been attached to
> the IOMMU, and the IOMMU driver might not expect FQ domains at
> ops->attach_dev() time.
> 
> Ensure that we immediately clamp FQ domains to plain DMA if not
> supported by the driver at device attach time, not later.
> 
> This regressed apple-dart in v6.5.
> [...]

Thanks for the report. To be sure the issue doesn't fall through the
cracks unnoticed, I'm adding it to regzbot, the Linux kernel regression
tracking bot:

#regzbot ^introduced a4fdd9762272
#regzbot title iommu: apple-dart regressed
#regzbot monitor:
https://lore.kernel.org/all/20230922-iommu-type-regression-v2-1-689b2ba9b673@marcan.st/
#regzbot fix: iommu/apple-dart: Handle DMA_FQ domains in attach_dev()
#regzbot ignore-activity

This isn't a regression? This issue or a fix for it are already
discussed somewhere else? It was fixed already? You want to clarify when
the regression started to happen? Or point out I got the title or
something else totally wrong? Then just reply and tell me -- ideally
while also telling regzbot about it, as explained by the page listed in
the footer of this mail.

Developers: When fixing the issue, remember to add 'Link:' tags pointing
to the report (the parent of this mail). See page linked in footer for
details.

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
--
Everything you wanna know about Linux kernel regression tracking:
https://linux-regtracking.leemhuis.info/about/#tldr
That page also explains what to do if mails like this annoy you.