[PATCH v4 0/5] Add generic data patching functions

[Benjamin Gray <bgray@linux.ibm.com>]

Currently patch_instruction() bases the write length on the value being
written. If the value looks like a prefixed instruction it writes 8 bytes,
otherwise it writes 4 bytes. This makes it potentially buggy to use for
writing arbitrary data, as if you want to write 4 bytes but it decides to
write 8 bytes it may clobber the following memory or be unaligned and
trigger an oops if it tries to cross a page boundary.

To solve this, this series pulls out the size parameter to the 'top' of
the memory patching logic, and propagates it through the various functions.

The two sizes supported are int and long; this allows for patching
instructions and pointers on both ppc32 and ppc64. On ppc32 these are the
same size, so care is taken to only use the size parameter on static
functions, so the compiler can optimise it out entirely. Unfortunately
GCC trips over its own feet here and won't optimise in a way that is
optimal for strict RWX (mpc85xx_smp_defconfig) and no RWX
(pmac32_defconfig). More details in the v2 cover letter.

Changes from v3:
  * Improved the boot test. Now that alignment is enforced,
    it checks the word (but not doubleword) aligned patch_ulong().

Changes from v2:
  * Various changes noted on each patch
  * Data patching now enforced to be aligned
  * Restore page aligned flushing optimisation

Changes from v1:
  * Addressed the v1 review actions
  * Removed noinline (for now)

v3: https://patchwork.ozlabs.org/project/linuxppc-dev/cover/20240325055302.876434-1-bgray@linux.ibm.com/
v2: https://patchwork.ozlabs.org/project/linuxppc-dev/cover/20231016050147.115686-1-bgray@linux.ibm.com/
v1: https://patchwork.ozlabs.org/project/linuxppc-dev/cover/20230207015643.590684-1-bgray@linux.ibm.com/

Benjamin Gray (5):
  powerpc/code-patching: Add generic memory patching
  powerpc/code-patching: Add data patch alignment check
  powerpc/64: Convert patch_instruction() to patch_u32()
  powerpc/32: Convert patch_instruction() to patch_uint()
  powerpc/code-patching: Add boot selftest for data patching

 arch/powerpc/include/asm/code-patching.h | 37 +++++++++++++
 arch/powerpc/kernel/module_64.c          |  5 +-
 arch/powerpc/kernel/static_call.c        |  2 +-
 arch/powerpc/lib/code-patching.c         | 70 +++++++++++++++++++-----
 arch/powerpc/lib/test-code-patching.c    | 41 ++++++++++++++
 arch/powerpc/platforms/powermac/smp.c    |  2 +-
 6 files changed, 137 insertions(+), 20 deletions(-)

--
2.45.0