On Thu, 10 Sep 2020 at 14:33, Tom Murphy [off-list ref] wrote:

On Wed, 9 Sep 2020 at 13:56, Tvrtko Ursulin
[off-list ref] wrote:

quoted

On 09/09/2020 10:16, Tvrtko Ursulin wrote:

quoted

On 08/09/2020 23:43, Tom Murphy wrote:

quoted

On Tue, 8 Sep 2020 at 16:56, Tvrtko Ursulin
[off-list ref] wrote:

quoted

On 08/09/2020 16:44, Logan Gunthorpe wrote:

quoted

On 2020-09-08 9:28 a.m., Tvrtko Ursulin wrote:

quoted

quoted

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.

quoted

quoted

+               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.

quoted

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!

quoted

Regards,

Tvrtko

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