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 11:27:15 +0100
From:   Christoph Hellwig <hch@....de>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Mathias Nyman <mathias.nyman@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Christoph Hellwig <hch@....de>,
        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 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.