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 11:31:02 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     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

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.

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.

Regards,

Hans