linux-kernel - Re: [Intel-gfx] [PATCH v3 0/6] Convert the intel iommu driver to the dma-iommu api

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Date:   Tue, 22 Sep 2020 12:45:52 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Robin Murphy <robin.murphy@....com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>, Tom Murphy <murphyt7@....ie>,
        David Woodhouse <dwmw2@...radead.org>,
        Christoph Hellwig <hch@...radead.org>
Cc:     Intel-gfx@...ts.freedesktop.org, Ashok Raj <ashok.raj@...el.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [Intel-gfx] [PATCH v3 0/6] Convert the intel iommu driver to the
 dma-iommu api



On 2020-09-22 3:51 a.m., Robin Murphy wrote:
> On 2020-09-18 21:47, Logan Gunthorpe wrote:
>> Hi Lu,
>>
>> On 2020-09-11 9:21 p.m., Lu Baolu wrote:
>>> Tom Murphy has almost done all the work. His latest patch series was
>>> posted here.
>>>
>>> https://lore.kernel.org/linux-iommu/20200903201839.7327-1-murphyt7@tcd.ie/
>>>
>>> Thanks a lot!
>>>
>>> This series is a follow-up with below changes:
>>>
>>> 1. Add a quirk for the i915 driver issue described in Tom's cover
>>> letter.
>>> 2. Fix several bugs in patch "iommu: Allow the dma-iommu api to use
>>> bounce buffers" to make the bounce buffer work for untrusted devices.
>>> 3. Several cleanups in iommu/vt-d driver after the conversion.
>>>
>>
>> I'm trying to test this on an old Sandy Bridge, but found that I get
>> spammed with warnings on boot. I've put a sample of a few of them below.
>> They all seem to be related to ioat.
>>
>> I had the same issue with Tom's v2 but never saw this on his v1.
> 
> I think this might have more to do with ioat being totally broken - 
> AFAICS it appears to allocate descriptors with a size of 2MB, but free 
> them with a size of 512KB. Try throwing CONFIG_DMA_API_DEBUG at it to 
> confirm.

Ah, yes, nice catch. Looks like it was broken recently by the following
commit, but nobody noticed and the dma-iommu patch set added a warning
which caught it.

a02254f8a676 ("dmaengine: ioat: Decreasing allocation chunk size 2M->512K")

Reverting that fixes the issue. I'll try to send patch or two for this.

Logan