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From:   Tom Murphy <murphyt7@tcd.ie>
Date:   Thu, 10 Sep 2020 14:33:43 +0100
Message-ID: <CALQxJus4prs0T6G9Z4bw5BDgwmkaiynBcoknLsYEY45SNZ6Ukg@mail.gmail.com>
Subject: Re: [Intel-gfx] [PATCH 0/8] Convert the intel iommu driver to the
 dma-iommu api
To:     Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc:     kvm@vger.kernel.org, David Airlie <airlied@linux.ie>,
        dri-devel@lists.freedesktop.org,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
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        iommu@lists.linux-foundation.org, Kukjin Kim <kgene@kernel.org>,
        Logan Gunthorpe <logang@deltatee.com>
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On Wed, 9 Sep 2020 at 13:56, Tvrtko Ursulin
<tvrtko.ursulin@linux.intel.com> wrote:
>
>
> On 09/09/2020 10:16, Tvrtko Ursulin wrote:
> > On 08/09/2020 23:43, Tom Murphy wrote:
> >> On Tue, 8 Sep 2020 at 16:56, Tvrtko Ursulin
> >> <tvrtko.ursulin@linux.intel.com> wrote:
> >>> On 08/09/2020 16:44, Logan Gunthorpe wrote:
> >>>> On 2020-09-08 9:28 a.m., Tvrtko Ursulin wrote:
> >>>>>>
> >>>>>> diff --git a/drivers/gpu/drm/i915/i915_scatterlist.h
> >>>>>> b/drivers/gpu/drm/i915/i915
> >>>>>> index b7b59328cb76..9367ac801f0c 100644
> >>>>>> --- a/drivers/gpu/drm/i915/i915_scatterlist.h
> >>>>>> +++ b/drivers/gpu/drm/i915/i915_scatterlist.h
> >>>>>> @@ -27,13 +27,19 @@ static __always_inline struct sgt_iter {
> >>>>>>     } __sgt_iter(struct scatterlist *sgl, bool dma) {
> >>>>>>            struct sgt_iter s = { .sgp = sgl };
> >>>>>>
> >>>>>> +       if (sgl && !sg_dma_len(s.sgp))
> >>>>>
> >>>>> I'd extend the condition to be, just to be safe:
> >>>>>       if (dma && sgl && !sg_dma_len(s.sgp))
> >>>>>
> >>>>
> >>>> Right, good catch, that's definitely necessary.
> >>>>
> >>>>>> +               s.sgp = NULL;
> >>>>>> +
> >>>>>>            if (s.sgp) {
> >>>>>>                    s.max = s.curr = s.sgp->offset;
> >>>>>> -               s.max += s.sgp->length;
> >>>>>> -               if (dma)
> >>>>>> +
> >>>>>> +               if (dma) {
> >>>>>> +                       s.max += sg_dma_len(s.sgp);
> >>>>>>                            s.dma = sg_dma_address(s.sgp);
> >>>>>> -               else
> >>>>>> +               } else {
> >>>>>> +                       s.max += s.sgp->length;
> >>>>>>                            s.pfn = page_to_pfn(sg_page(s.sgp));
> >>>>>> +               }
> >>>>>
> >>>>> Otherwise has this been tested or alternatively how to test it?
> >>>>> (How to
> >>>>> repro the issue.)
> >>>>
> >>>> It has not been tested. To test it, you need Tom's patch set without
> >>>> the
> >>>> last "DO NOT MERGE" patch:
> >>>>
> >>>> https://lkml.kernel.org/lkml/20200907070035.GA25114@infradead.org/T/
> >>>
> >>> Tom, do you have a branch somewhere I could pull from? (Just being lazy
> >>> about downloading a bunch of messages from the archives.)
> >>
> >> I don't unfortunately. I'm working locally with poor internet.
> >>
> >>>
> >>> What GPU is in your Lenovo x1 carbon 5th generation and what
> >>> graphical/desktop setup I need to repro?
> >>
> >>
> >> Is this enough info?:
> >>
> >> $ lspci -vnn | grep VGA -A 12
> >> 00:02.0 VGA compatible controller [0300]: Intel Corporation HD
> >> Graphics 620 [8086:5916] (rev 02) (prog-if 00 [VGA controller])
> >>      Subsystem: Lenovo ThinkPad X1 Carbon 5th Gen [17aa:224f]
> >>      Flags: bus master, fast devsel, latency 0, IRQ 148
> >>      Memory at eb000000 (64-bit, non-prefetchable) [size=16M]
> >>      Memory at 60000000 (64-bit, prefetchable) [size=256M]
> >>      I/O ports at e000 [size=64]
> >>      [virtual] Expansion ROM at 000c0000 [disabled] [size=128K]
> >>      Capabilities: [40] Vendor Specific Information: Len=0c <?>
> >>      Capabilities: [70] Express Root Complex Integrated Endpoint, MSI 00
> >>      Capabilities: [ac] MSI: Enable+ Count=1/1 Maskable- 64bit-
> >>      Capabilities: [d0] Power Management version 2
> >>      Capabilities: [100] Process Address Space ID (PASID)
> >>      Capabilities: [200] Address Translation Service (ATS)
> >
> > Works for a start. What about the steps to repro? Any desktop
> > environment and it is just visual corruption, no hangs/stalls or such?
> >
> > I've submitted a series consisting of what I understood are the patches
> > needed to repro the issue to our automated CI here:
> >
> > https://patchwork.freedesktop.org/series/81489/
> >
> > So will see if it will catch something, or more targeted testing will be
> > required. Hopefully it does trip over in which case I can add the patch
> > suggested by Logan on top and see if that fixes it. Or I'll need to
> > write a new test case.
> >
> > If you could glance over my series to check I identified the patches
> > correctly it would be appreciated.
>
> Our CI was more than capable at catching the breakage so I've copied you
> on a patch (https://patchwork.freedesktop.org/series/81497/) which has a
> good potential to fix this. (Or improve the robustness of our sg walks,
> depends how you look at it.)
>
> Would you be able to test it in your environment by any chance? If it
> works I understand it unblocks your IOMMU work, right?

I tested your latest patch set ([PATCH 1/2] drm/i915: Fix DMA mapped
scatterlist walks) and it fixes the issue. great work!

>
> Regards,
>
> Tvrtko