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From:   Tom Yan <tom.ty89@gmail.com>
Date:   Sat, 28 Nov 2020 09:25:03 +0800
Message-ID: <CAGnHSEmyrw=r56ocLCkia+sYT0tmcCScZitBi=G+DY=gRBy+sg@mail.gmail.com>
Subject: Re: 5.10 regression caused by: "uas: fix sdev->host->dma_dev": many
 XHCI swiotlb buffer is full / DMAR: Device bounce map failed errors on
 thunderbolt connected XHCI controller
To:     Hans de Goede <hdegoede@redhat.com>
Cc:     Christoph Hellwig <hch@lst.de>,
        Mathias Nyman <mathias.nyman@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-usb <linux-usb@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-pci@vger.kernel.org, Lu Baolu <baolu.lu@linux.intel.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Should we still be clamping max_sectors to dma_max_mapping_size(dev)
(for now)? with dev being us->pusb_dev->bus->sysdev and
devinfo->udev->bus->sysdev respectively (i.e. revert only
scsi_add_host_with_dma() to scsi_add_host())?

On Sat, 28 Nov 2020 at 02:12, Hans de Goede <hdegoede@redhat.com> wrote:
>
> Hi,
>
> On 11/27/20 5:19 PM, Christoph Hellwig wrote:
> > On Fri, Nov 27, 2020 at 01:32:16PM +0100, Hans de Goede wrote:
> >> I ran some more tests, I can confirm that reverting:
> >>
> >> 5df7ef7d32fe "uas: bump hw_max_sectors to 2048 blocks for SS or faster drives"
> >> 558033c2828f "uas: fix sdev->host->dma_dev"
> >>
> >> Makes the problem go away while running a 5.10 kernel. I also tried doubling
> >> the swiotlb size by adding: swiotlb=65536 to the kernel commandline but that
> >> does not help.
> >>
> >> Some more observations:
> >>
> >> 1. The usb-storage driver does not cause this issue, even though it has a
> >> very similar change.
> >>
> >> 2. The problem does not happen until I plug an UAS decvice into the dock.
> >>
> >> 3. The problem continues to happen even after I unplug the UAS device and
> >> rmmod the uas module
> >>
> >> 3. made me take a bit closer look to the troublesome commit, it passes:
> >> udev->bus->sysdev, which I assume is the XHCI controller itself as device
> >> to scsi_add_host_with_dma, which in turn seems to cause permanent changes
> >> to the dma settings for the XHCI controller. I'm not all that familiar with
> >> the DMA APIs but I'm getting the feeling that passing the actual XHCI-controller's
> >> device as dma-device to scsi_add_host_with_dma is simply the wrong thing to
> >> do; and that the intended effects (honor XHCI dma limits, but do not cause
> >> any changes the XHCI dma settings) should be achieved differently.
> >>
> >> Note that if this is indeed wrong, the matching usb-storage change should
> >> likely also be dropped.
> >
> > One problem in this area is that the clamping of the DMA size through
> > dma_max_mapping_size mentioned in the commit log doesn't work when
> > swiotlb is called from intel-iommu. I think we need to wire up those
> > calls there as well.
>
> Ok, but that does not sound like a quick last minute fix for 5.10, so maybe
> for 5.10 we should just revert the uas and usb-storage changes which trigger
> this problem and then retry those for 5.11 ?
>
> Regards,
>
> Hans
>