[Intel-gfx] [PATCH v2 0/2] drm/i915: Failsafe migration blits

Thomas Hellström
2021-11-01T19:13:53Z

This patch series introduces failsafe migration blits.
The reason for this seemingly strange concept is that if the initial
clearing or readback of LMEM fails for some reason[1], and we then set up
either GPU- or CPU ptes to the allocated LMEM, we can expose old
contents from other clients.

So after each migration blit to LMEM, attach a dma-fence callback that
checks the migration fence error value and if it's an error,
performs a memcpy blit, instead.

Patch 1 splits out the TTM move code into separate files
Patch 2 implements the failsafe blits and related self-tests

[1] There are at least two ways we could trigger exposure of uninitialized
LMEM assuming the migration blits themselves never trigger a gpu hang.

a) A gpu operation preceding a pipelined eviction blit resets and sets the
error fence to -EIO, and the error is propagated across the TTM manager to
the clear / swapin blit of a newly allocated TTM resource. It aborts and
leaves the memory uninitialized.

b) Something wedges the GT while a migration blit is submitted. It ends up
never executed and TTM can fault user-space cpu-ptes into uninitialized
memory.

Thomas Hellström (2):
drm/i915/ttm: Reorganize the ttm move code
drm/i915/ttm: Failsafe migration blits

drivers/gpu/drm/i915/Makefile | 1 +
drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 328 ++---------
drivers/gpu/drm/i915/gem/i915_gem_ttm.h | 35 ++
drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c | 520 ++++++++++++++++++
drivers/gpu/drm/i915/gem/i915_gem_ttm_move.h | 43 ++
.../drm/i915/gem/selftests/i915_gem_migrate.c | 24 +-
6 files changed, 670 insertions(+), 281 deletions(-)
create mode 100644 drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
create mode 100644 drivers/gpu/drm/i915/gem/i915_gem_ttm_move.h

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2.31.1