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

[Logan Gunthorpe]

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@xxxxxx/
>>>
>>> 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