[PATCH v4 0/4] Upgrade READ_ONCE() to RCpc acquire on arm64 with LTO

[Will Deacon]

Hi all,

These patches were previously posted as part of a larger series enabling
architectures to override __READ_ONCE():

  v3: https://lore.kernel.org/lkml/20200710165203.31284-1-will@xxxxxxxxxx/

With the bulk of that merged, the four patches here override READ_ONCE()
so that it gains RCpc acquire semantics on arm64 when LTO is enabled. We
can revisit this as and when the compiler provides a means for us to reason
about the result of dependency-breaking optimisations. In the meantime,
this unblocks LTO for arm64, which I would really like to see merged so
that we can focus on enabling CFI.

I plan to queue these on their own branch in the arm64 tree for 5.11 at
-rc3.

Cheers,

Will

Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx

--->8

Will Deacon (4):
  arm64: alternatives: Split up alternative.h
  arm64: cpufeatures: Add capability for LDAPR instruction
  arm64: alternatives: Remove READ_ONCE() usage during patch operation
  arm64: lto: Strengthen READ_ONCE() to acquire when CONFIG_LTO=y

 arch/arm64/Kconfig                          |   3 +
 arch/arm64/include/asm/alternative-macros.h | 276 ++++++++++++++++++++
 arch/arm64/include/asm/alternative.h        | 267 +------------------
 arch/arm64/include/asm/cpucaps.h            |   3 +-
 arch/arm64/include/asm/insn.h               |   3 +-
 arch/arm64/include/asm/rwonce.h             |  63 +++++
 arch/arm64/kernel/alternative.c             |   7 +-
 arch/arm64/kernel/cpufeature.c              |  10 +
 arch/arm64/kernel/vdso/Makefile             |   2 +-
 arch/arm64/kernel/vdso32/Makefile           |   2 +-
 arch/arm64/kernel/vmlinux.lds.S             |   2 +-
 11 files changed, 364 insertions(+), 274 deletions(-)
 create mode 100644 arch/arm64/include/asm/alternative-macros.h
 create mode 100644 arch/arm64/include/asm/rwonce.h

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2.29.1.341.ge80a0c044ae-goog