[PATCH v9 0/2] Renovate memcpy_mcsafe with copy_mc_to_{user, kernel}

* [PATCH v9 0/2] Renovate memcpy_mcsafe with copy_mc_to_{user, kernel}
@ 2020-09-23 16:41 ` Dan Williams
  0 siblings, 0 replies; 22+ messages in thread
From: Dan Williams @ 2020-09-23 16:41 UTC (permalink / raw)
  To: mingo
  Cc: Tony Luck, Peter Zijlstra, Linus Torvalds, Alexander Viro,
	Borislav Petkov, stable, x86, H. Peter Anvin, tglx,
	Andy Lutomirski, Paul Mackerras, Benjamin Herrenschmidt,
	Erwin Tsaur, Michael Ellerman, Mikulas Patocka,
	Arnaldo Carvalho de Melo, 0day robot, linux-nvdimm, linux-kernel,
	jack

Changes since v8 [1]:
- Rebase on v5.9-rc6

- Fix a performance regression in the x86 copy_mc_to_user()
  implementation that was duplicating copies in the "fragile" case.

- Refreshed the cover letter.

[1]: http://lore.kernel.org/r/159630255616.3143511.18110575960499749012.stgit@dwillia2-desk3.amr.corp.intel.com

---

The motivations to go rework memcpy_mcsafe() are that the benefit of
doing slow and careful copies is obviated on newer CPUs, and that the
current opt-in list of cpus to instrument recovery is broken relative to
those cpus.  There is no need to keep an opt-in list up to date on an
ongoing basis if pmem/dax operations are instrumented for recovery by
default. With recovery enabled by default the old "mcsafe_key" opt-in to
careful copying can be made a "fragile" opt-out. Where the "fragile"
list takes steps to not consume poison across cachelines.

The discussion with Linus made clear that the current "_mcsafe" suffix
was imprecise to a fault. The operations that are needed by pmem/dax are
to copy from a source address that might throw #MC to a destination that
may write-fault, if it is a user page. So copy_to_user_mcsafe() becomes
copy_mc_to_user() to indicate the separate precautions taken on source
and destination. copy_mc_to_kernel() is introduced as a version that
does not expect write-faults on the destination, but is still prepared
to abort with an error code upon taking #MC.

These patches have received a kbuild-robot build success notification
across 114 configs, the rebase to v5.9-rc6 did not encounter any
conflicts, and the merge with tip/master is conflict-free.

---

Dan Williams (2):
      x86, powerpc: Rename memcpy_mcsafe() to copy_mc_to_{user,kernel}()
      x86/copy_mc: Introduce copy_mc_generic()

 arch/powerpc/Kconfig                               |    2 
 arch/powerpc/include/asm/string.h                  |    2 
 arch/powerpc/include/asm/uaccess.h                 |   40 +++--
 arch/powerpc/lib/Makefile                          |    2 
 arch/powerpc/lib/copy_mc_64.S                      |    4 
 arch/x86/Kconfig                                   |    2 
 arch/x86/Kconfig.debug                             |    2 
 arch/x86/include/asm/copy_mc_test.h                |   75 +++++++++
 arch/x86/include/asm/mcsafe_test.h                 |   75 ---------
 arch/x86/include/asm/string_64.h                   |   32 ----
 arch/x86/include/asm/uaccess.h                     |   21 +++
 arch/x86/include/asm/uaccess_64.h                  |   20 --
 arch/x86/kernel/cpu/mce/core.c                     |    8 -
 arch/x86/kernel/quirks.c                           |    9 -
 arch/x86/lib/Makefile                              |    1 
 arch/x86/lib/copy_mc.c                             |   65 ++++++++
 arch/x86/lib/copy_mc_64.S                          |  165 ++++++++++++++++++++
 arch/x86/lib/memcpy_64.S                           |  115 --------------
 arch/x86/lib/usercopy_64.c                         |   21 ---
 drivers/md/dm-writecache.c                         |   15 +-
 drivers/nvdimm/claim.c                             |    2 
 drivers/nvdimm/pmem.c                              |    6 -
 include/linux/string.h                             |    9 -
 include/linux/uaccess.h                            |    9 +
 include/linux/uio.h                                |   10 +
 lib/Kconfig                                        |    7 +
 lib/iov_iter.c                                     |   43 +++--
 tools/arch/x86/include/asm/mcsafe_test.h           |   13 --
 tools/arch/x86/lib/memcpy_64.S                     |  115 --------------
 tools/objtool/check.c                              |    5 -
 tools/perf/bench/Build                             |    1 
 tools/perf/bench/mem-memcpy-x86-64-lib.c           |   24 ---
 tools/testing/nvdimm/test/nfit.c                   |   48 +++---
 .../testing/selftests/powerpc/copyloops/.gitignore |    2 
 tools/testing/selftests/powerpc/copyloops/Makefile |    6 -
 .../selftests/powerpc/copyloops/copy_mc_64.S       |    1 
 .../selftests/powerpc/copyloops/memcpy_mcsafe_64.S |    1 
 37 files changed, 452 insertions(+), 526 deletions(-)
 rename arch/powerpc/lib/{memcpy_mcsafe_64.S => copy_mc_64.S} (98%)
 create mode 100644 arch/x86/include/asm/copy_mc_test.h
 delete mode 100644 arch/x86/include/asm/mcsafe_test.h
 create mode 100644 arch/x86/lib/copy_mc.c
 create mode 100644 arch/x86/lib/copy_mc_64.S
 delete mode 100644 tools/arch/x86/include/asm/mcsafe_test.h
 delete mode 100644 tools/perf/bench/mem-memcpy-x86-64-lib.c
 create mode 120000 tools/testing/selftests/powerpc/copyloops/copy_mc_64.S
 delete mode 120000 tools/testing/selftests/powerpc/copyloops/memcpy_mcsafe_64.S

base-commit: ba4f184e126b751d1bffad5897f263108befc780
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