linux-kernel - Re: [Intel-gfx] [PATCH 0/8] Convert the intel iommu driver to the dma-iommu api

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Date:   Thu, 10 Sep 2020 14:34:38 +0100
From:   Tom Murphy <murphyt7@....ie>
To:     Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
Cc:     kvm@...r.kernel.org, David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Julien Grall <julien.grall@....com>,
        Will Deacon <will@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        linux-samsung-soc@...r.kernel.org, Marc Zyngier <maz@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        linux-rockchip@...ts.infradead.org, Andy Gross <agross@...nel.org>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>,
        linux-s390@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org,
        Robin Murphy <robin.murphy@....com>,
        linux-mediatek@...ts.infradead.org, linux-tegra@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        virtualization@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org,
        David Woodhouse <dwmw2@...radead.org>,
        Cornelia Huck <cohuck@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        iommu@...ts.linux-foundation.org, Kukjin Kim <kgene@...nel.org>,
        Logan Gunthorpe <logang@...tatee.com>
Subject: Re: [Intel-gfx] [PATCH 0/8] Convert the intel iommu driver to the
 dma-iommu api

On Thu, 10 Sep 2020 at 14:33, Tom Murphy <murphyt7@....ie> wrote:
>
> On Wed, 9 Sep 2020 at 13:56, Tvrtko Ursulin
> <tvrtko.ursulin@...ux.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@...ux.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?

And yes this does unblock the iommu work

>
> 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