linux-kernel - Re: 5.10 regression, many XHCI swiotlb buffer is full / DMAR: Device bounce map failed errors on thunderbolt connected XHCI controller

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Date:   Tue, 24 Nov 2020 14:17:19 +0200
From:   Mathias Nyman <mathias.nyman@...ux.intel.com>
To:     Hans de Goede <hdegoede@...hat.com>, Christoph Hellwig <hch@....de>
Cc:     Mathias Nyman <mathias.nyman@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb <linux-usb@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-pci@...r.kernel.org
Subject: Re: 5.10 regression, many XHCI swiotlb buffer is full / DMAR: Device
 bounce map failed errors on thunderbolt connected XHCI controller

On 24.11.2020 12.31, Hans de Goede wrote:
> Hi,
> 
> On 11/24/20 11:27 AM, Christoph Hellwig wrote:
>> On Mon, Nov 23, 2020 at 03:49:09PM +0100, Hans de Goede wrote:
>>> Hi,
>>>
>>> +Cc Christoph Hellwig <hch@....de>
>>>
>>> Christoph, this is still an issue, so I've been looking around a bit and think this
>>> might have something to do with the dma-mapping-5.10 changes.
>>>
>>> Do you have any suggestions to debug this, or is it time to do a git bisect
>>> on this before 5.10 ships with regression?
>>
>> Given that DMAR prefix this seems to be about using intel-iommu + bounce
>> buffering for external devices.  I can't really think of anything specific
>> in 5.10 related to that, so maybe you'll need to bisect.
>>
>> I doub this means we are actually leaking swiotlb buffers, so while
>> I'm pretty sure we broke something in lower layers this also means
>> xhci doesn't handle swiotlb operation very gracefully in general.

Can't think of any xhci change since 5.9 that would cause this.
It's possible there's some underlying xhci issue the 5.10 dma-mapping
changes reveal.

> 
> Ok, I've re-arranged my schedule a bit so that I have time to bisect this
> tomorrow, so with some luck I will be able to provide info on which commit
> introduced this issue tomorrow around the end of the day.

Thanks for looking into it.

-Mathias