[PATCH v6 0/2] drm/i915: add guard page to ggtt->error_capture

[Andrzej Hajda <andrzej.hajda@intel.com>]

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
v6:
    - use scratch_range

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

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

---
- Link to v5: https://lore.kernel.org/r/20230308-guard_error_capture-v5-0-6d1410d13540@intel.com

---
Andrzej Hajda (2):
      drm/i915/gt: introduce vm->scratch_range callback
      drm/i915: add guard page to ggtt->error_capture

 drivers/gpu/drm/i915/gt/intel_ggtt.c      | 43 ++++++++++++++++++++++++++++---
 drivers/gpu/drm/i915/gt/intel_ggtt_gmch.c |  1 +
 drivers/gpu/drm/i915/gt/intel_gtt.h       |  2 ++
 3 files changed, 42 insertions(+), 4 deletions(-)
---
base-commit: 3cd6c251f39c14df9ab711e3eb56e703b359ff54
change-id: 20230308-guard_error_capture-f3f334eec85f

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