[PATCH v3 0/3] HMM tests and minor fixes

[Ralph Campbell]

These changes are based on Jason's rdma/hmm branch (5.4.0-rc1).
Patch 1 was previously posted here [1] but was dropped from that orginal
series. Hopefully, the tests will reduce concerns about edge conditions.
I'm sure more tests could be usefully added but I thought this was a good
starting point.

Changes since v2:
patch 1:
Removed hmm_range_needs_fault() and just use hmm_range_need_fault().
Updated the change log to include that it fixes a bug where
hmm_range_fault() incorrectly returned an error when no fault is requested.
patch 2:
Removed the confusing change log wording about DMA.
Changed hmm_range_fault() to return the PFN of the zero page like any other
page.
patch 3:
Adjusted the test code to match the new zero page behavior.

Changes since v1:
Rebased to Jason's rdma/hmm branch (5.4.0-rc1).
Cleaned up locking for the test driver's page tables.
Incorporated Christoph Hellwig's comments.

[1] https://lore.kernel.org/linux-mm/20190726005650.2566-6-rcampbell@xxxxxxxxxx/

Ralph Campbell (3):
  mm/hmm: make full use of walk_page_range()
  mm/hmm: allow snapshot of the special zero page
  mm/hmm/test: add self tests for HMM

 MAINTAINERS                            |    3 +
 drivers/char/Kconfig                   |   11 +
 drivers/char/Makefile                  |    1 +
 drivers/char/hmm_dmirror.c             | 1566 ++++++++++++++++++++++++
 include/Kbuild                         |    1 +
 include/uapi/linux/hmm_dmirror.h       |   74 ++
 mm/hmm.c                               |  136 +-
 tools/testing/selftests/vm/.gitignore  |    1 +
 tools/testing/selftests/vm/Makefile    |    3 +
 tools/testing/selftests/vm/config      |    3 +
 tools/testing/selftests/vm/hmm-tests.c | 1311 ++++++++++++++++++++
 tools/testing/selftests/vm/run_vmtests |   16 +
 tools/testing/selftests/vm/test_hmm.sh |   97 ++
 13 files changed, 3158 insertions(+), 65 deletions(-)
 create mode 100644 drivers/char/hmm_dmirror.c
 create mode 100644 include/uapi/linux/hmm_dmirror.h
 create mode 100644 tools/testing/selftests/vm/hmm-tests.c
 create mode 100755 tools/testing/selftests/vm/test_hmm.sh

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2.20.1