In the Linux kernel, the following vulnerability has been resolved: drm/xe/shrinker: Take a runtime PM ref before shrinking non-system memo

In the Linux kernel, the following vulnerability has been resolved:

drm/xe/shrinker: Take a runtime PM ref before shrinking non-system memory

__xe_shrinker_walk() walks the SYSTEM and TT LRUs without a runtime PM
reference. Shrinking a bo outside system memory invalidates its GPU
mappings, which needs the device resumed, so while it is runtime
suspended the page table zap trips an assert and the TLB invalidation
returns -ENODEV:

WARNING: drivers/gpu/drm/xe/xe_bo.c:770 at xe_bo_move_notify+0x1fc/0x450 [xe]
xe_bo_shrink+0x20f/0x2b0 [xe]
__xe_shrinker_walk+0x174/0x410 [xe]
xe_shrinker_scan+0x10c/0x1e0 [xe]
do_shrink_slab+0x176/0x7e0
drop_caches_sysctl_handler+0x9c/0xf0

Take a reference before walking a memory type other than XE_PL_SYSTEM
and stop there if it cannot be acquired. Reuse the shrinker's existing
acquire path, which resumes the device directly where reclaim allows
that and otherwise queues the PM worker for a later scan. Stop the walk
once the scan target is met, so a satisfied scan does not wake the
device. System memory is still reclaimed while the device is suspended.

Gate this on xe_device_is_l2_flush_optimized(), the same condition under
which xe_bo_trigger_rebind() issues the invalidation for a non-fault-mode
vm, so reclaim is unaffected elsewhere. The System CCS copy already has
its own reference in xe_bo_shrink().

Only a non-fault-mode vm can reach this, since a fault-mode vm requires
LR mode and that holds a runtime PM reference for the vm's lifetime.

Reproduced with igt@xe_madvise@dontneed-before-exec while the GPU is
runtime suspended.

v2: simplify needs_rpm check. (Matt)
retarget Fixes tag since the issue occurs with the non-fault-mode
path added by 4e7ebff69aed.
v3: handle this in xe_shrinker.c instead of xe_bo.c (Thomas)
v4: stop the walk once the scan target is met. (Sashiko)
v5: rebase on the freed page accounting fix. (Sashiko)
v6: reuse the shrinker acquire path so runtime pm can be resumed
directly instead of always queueing a worker. (Thomas)
v7: replace xe_pm_runtime_put() with xe_shrinker_runtime_pm_put(). (Thomas)

(cherry picked from commit 628f92b28bf4c371c10207daf6fc4caee0c0db2e)