[PATCH v2 0/9] drm/i915: Replace kmap_atomic() with kmap_local_page()

[Zhao Liu]

From: Zhao Liu <zhao1.liu at intel.com>

Hi list,

Sorry for a long delay since v1 [1]. This patchset is based on 197b6b6
(Linux 6.3-rc4).

Welcome and thanks for your review and comments!


# Purpose of this patchset

The purpose of this pacthset is to replace all uses of kmap_atomic() in
i915 with kmap_local_page() because the use of kmap_atomic() is being
deprecated in favor of kmap_local_page()[1]. And 92b64bd (mm/highmem:
add notes about conversions from kmap{,_atomic}()) has declared the
deprecation of kmap_atomic().


# Motivation for deprecating kmap_atomic() and using kmap_local_page()

The main difference between atomic and local mappings is that local
mappings doesn't disable page faults or preemption (the preemption is
disabled for !PREEMPT_RT case, otherwise it only disables migration).

With kmap_local_page(), we can avoid the often unwanted side effect of
unnecessary page faults and preemption disables.


# Patch summary

Patch 1, 4-6 and 8-9 replace kamp_atomic()/kunmap_atomic() with
        kmap_local_page()/kunmap_local() directly. With thses local
        mappings, the page faults and preemption are allowed.

Patch 2 and 7 use memcpy_from_page() and memcpy_to_page() to replace
        kamp_atomic()/kunmap_atomic(). These two variants of memcpy()
        are based on the local mapping, so page faults and preemption
        are also allowed in these two interfaces.

Patch 3 replaces kamp_atomic()/kunmap_atomic() with kmap_local_page()/
        kunmap_local() and also diable page fault since the for special
        handling (pls see the commit message).


# Changes since v1

* Dropped hot plug related description in commit message since it has
  nothing to do with kmap_local_page().
* Emphasized the motivation for using kmap_local_page() in commit
  message.
* Rebased patch 1 on f47e630 (drm/i915/gem: Typecheck page lookups) to
  keep the "idx" variable of type pgoff_t here.
* Used memcpy_from_page() and memcpy_to_page() to replace
  kmap_local_page() + memcpy() in patch 2.


# Reference

[1]: https://lore.kernel.org/lkml/20221017093726.2070674-1-zhao1.liu@linux.intel.com/
[1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com
---
Zhao Liu (9):
  drm/i915: Use kmap_local_page() in gem/i915_gem_object.c
  drm/i915: Use memcpy_[from/to]_page() in gem/i915_gem_pyhs.c
  drm/i915: Use kmap_local_page() in gem/i915_gem_shmem.c
  drm/i915: Use kmap_local_page() in gem/selftests/huge_pages.c
  drm/i915: Use kmap_local_page() in gem/selftests/i915_gem_coherency.c
  drm/i915: Use kmap_local_page() in gem/selftests/i915_gem_context.c
  drm/i915: Use memcpy_from_page() in gt/uc/intel_uc_fw.c
  drm/i915: Use kmap_local_page() in i915_cmd_parser.c
  drm/i915: Use kmap_local_page() in gem/i915_gem_execbuffer.c

 drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c       | 10 +++++-----
 drivers/gpu/drm/i915/gem/i915_gem_object.c           |  8 +++-----
 drivers/gpu/drm/i915/gem/i915_gem_phys.c             | 10 ++--------
 drivers/gpu/drm/i915/gem/i915_gem_shmem.c            |  6 ++++--
 drivers/gpu/drm/i915/gem/selftests/huge_pages.c      |  6 +++---
 .../gpu/drm/i915/gem/selftests/i915_gem_coherency.c  | 12 ++++--------
 .../gpu/drm/i915/gem/selftests/i915_gem_context.c    |  8 ++++----
 drivers/gpu/drm/i915/gt/uc/intel_uc_fw.c             |  5 +----
 drivers/gpu/drm/i915/i915_cmd_parser.c               |  4 ++--
 9 files changed, 28 insertions(+), 41 deletions(-)

-- 
2.34.1