Re: [bisected] 5.13-rc2 i915 regression in b12d691ea5e01d "i915: fix remap_io_sg to verify the pgprot"

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 19 May 2021, Sergei Trofimovich <slyfox@gentoo.org> wrote:
> Hi Christoph and i915 maintainers!
>
> vanilla 5.13-rc2 got some rendering regression on gen2(?) i915 chips:

293837b9ac8d ("Revert "i915: fix remap_io_sg to verify the pgprot"")
will be included in v5.13-rc3.

BR,
Jani.


>
>   In gtk apps cursor gets corrupted for a short period of time.
>
>   In firefox text selection and text scrolling shows artifacts for a short
>   time (seconds). As if tiny horisontal tiles (1 pixel high, ~20-50 pixels
>   long) fail to refresh in time.
>
>   I was not able get a screenshot with artifacts: pictures are always clean.
>   I can grab a photo or tiny video if needed.
>
> Bisection was straightforward and landed on:
>
> b12d691ea5e01db42ccf3b4207e57cb3ce7cfe91 is the first bad commit
> commit b12d691ea5e01db42ccf3b4207e57cb3ce7cfe91
> Author: Christoph Hellwig <hch@lst.de>
> Date:   Thu Apr 29 22:57:38 2021 -0700
>
>     i915: fix remap_io_sg to verify the pgprot
>
>     remap_io_sg claims that the pgprot is pre-verified using an io_mapping,
>     but actually does not get passed an io_mapping and just uses the pgprot in
>     the VMA.  Remove the apply_to_page_range abuse and just loop over
>     remap_pfn_range for each segment.
>
>     Note: this could use io_mapping_map_user by passing an iomap to
>     remap_io_sg if the maintainers can verify that the pgprot in the iomap in
>     the only caller is indeed the desired one here.
>
>     Link: https://lkml.kernel.org/r/20210326055505.1424432-5-hch@lst.de
>     Signed-off-by: Christoph Hellwig <hch@lst.de>
>     Cc: Chris Wilson <chris@chris-wilson.co.uk>
>     Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
>     Cc: Jani Nikula <jani.nikula@linux.intel.com>
>     Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
>     Cc: Peter Zijlstra <peterz@infradead.org>
>     Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
>     Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
>     Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
>
>  drivers/gpu/drm/i915/i915_mm.c | 73 +++++++++++++-----------------------------
>  1 file changed, 23 insertions(+), 50 deletions(-)
>
> System:
>     $ Linux sf 5.12.0-11146-g8ca5297e7e38 #302 SMP PREEMPT Thu Apr 29 23:30:52 BST 2021 x86_64 Intel(R) Core(TM) i7-2700K CPU @ 3.50GHz GenuineIntel GNU/Linux
>     $ lspci -v
>     00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09) (prog-if 00 [VGA controller])
>         Subsystem: Gigabyte Technology Co., Ltd 2nd Generation Core Processor Family Integrated Graphics Controller
>         Flags: bus master, fast devsel, latency 0, IRQ 27
>         Memory at f7800000 (64-bit, non-prefetchable) [size=4M]
>         Memory at e0000000 (64-bit, prefetchable) [size=256M]
>         I/O ports at f000 [size=64]
>         Expansion ROM at 000c0000 [virtual] [disabled] [size=128K]
>         Capabilities: [90] MSI: Enable+ Count=1/1 Maskable- 64bit-
>         Capabilities: [d0] Power Management version 2
>         Capabilities: [a4] PCI Advanced Features
>         Kernel driver in use: i915
>
> Software:
>     mesa-20.3.5 : i965 driver
>       glamor X acceleration enabled on Mesa DRI Intel(R) HD Graphics 3000 (SNB GT2)
>     xorg-server-1.20.11
>
> Thanks!

-- 
Jani Nikula, Intel Open Source Graphics Center