[PATCH v5 0/4] drm/i915: add guard page to ggtt->error_capture

[Andrzej Hajda]

This patch tries to diminish plague of DMAR read errors present
in CI for ADL*, RPL*, DG2 platforms, see for example [1] (grep DMAR).
CI is usually tolerant for these errors, so the scale of the problem
is not really visible.
To show it I have counted lines containing DMAR read errors in dmesgs
produced by CI for all three versions of the patch, but in contrast to v2
I have grepped only for lines containing "PTE Read access".
Below stats for kernel w/o patchset vs patched one.
v1: 210 vs 0
v2: 201 vs 0
v3: 214 vs 0
Apparently the patchset fixes all common PTE read errors.

Changelog:
v2:
    - modified commit message (I hope the diagnosis is correct),
    - added bug checks to ensure scratch is initialized on gen3 platforms.
      CI produces strange stacktrace for it suggesting scratch[0] is NULL,
      to be removed after resolving the issue with gen3 platforms.
v3:
    - removed bug checks, replaced with gen check.
v4:
    - change code for scratch page insertion to support all platforms,
    - add info in commit message there could be more similar issues
v5:
    - changed to patchset adding nop_clear_range related code,
    - re-insert scratch PTEs on resume

To: Jani Nikula <jani.nikula at linux.intel.com>
To: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
To: Rodrigo Vivi <rodrigo.vivi at intel.com>
To: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
Cc: intel-gfx at lists.freedesktop.org
Cc: dri-devel at lists.freedesktop.org
Cc: linux-kernel at vger.kernel.org
Cc: Andi Shyti <andi.shyti at linux.intel.com>
Cc: Chris Wilson <chris.p.wilson at linux.intel.com>
Cc: Nirmoy Das <nirmoy.das at intel.com>

Signed-off-by: Andrzej Hajda <andrzej.hajda at intel.com>

---
Andrzej Hajda (4):
      drm/i915/gt: make nop_clear_range public
      drm/i915/display: use nop_clear_range instead of local function
      drm/i915/selftests: use nop_clear_range instead of local function
      drm/i915: add guard page to ggtt->error_capture

 drivers/gpu/drm/i915/display/intel_dpt.c  |  7 +-----
 drivers/gpu/drm/i915/gt/intel_ggtt.c      | 38 ++++++++++++++++++++++++++-----
 drivers/gpu/drm/i915/gt/intel_gtt.h       |  2 ++
 drivers/gpu/drm/i915/selftests/mock_gtt.c |  9 ++------
 4 files changed, 37 insertions(+), 19 deletions(-)
---
base-commit: 3cd6c251f39c14df9ab711e3eb56e703b359ff54
change-id: 20230308-guard_error_capture-f3f334eec85f

Best regards,
-- 
Andrzej Hajda <andrzej.hajda at intel.com>