powerpc/lib/xor_vmx: Ensure no altivec code executes before enable_kernel_altivec()
authorMatt Brown <matthew.brown.dev@gmail.com>
Tue, 23 May 2017 23:45:59 +0000 (09:45 +1000)
committerMichael Ellerman <mpe@ellerman.id.au>
Fri, 2 Jun 2017 10:17:52 +0000 (20:17 +1000)
commitf718d426d7e42eec6e5d2932f52a51de23bd3b30
tree82c3b5b118929622eeeaa41d3f11402b6d9d8935
parent48a316e350974739235c234430ec0e129f864a43
powerpc/lib/xor_vmx: Ensure no altivec code executes before enable_kernel_altivec()

The xor_vmx.c file is used for the RAID5 xor operations. In these functions
altivec is enabled to run the operation and then disabled.

The code uses enable_kernel_altivec() around the core of the algorithm, however
the whole file is built with -maltivec, so the compiler is within its rights to
generate altivec code anywhere. This has been seen at least once in the wild:

  0:mon> di $xor_altivec_2
  c0000000000b97d0  3c4c01d9 addis   r2,r12,473
  c0000000000b97d4  3842db30 addi    r2,r2,-9424
  c0000000000b97d8  7c0802a6 mflr    r0
  c0000000000b97dc  f8010010 std     r0,16(r1)
  c0000000000b97e0  60000000 nop
  c0000000000b97e4  7c0802a6 mflr    r0
  c0000000000b97e8  faa1ffa8 std     r21,-88(r1)
  ...
  c0000000000b981c  f821ff41 stdu    r1,-192(r1)
  c0000000000b9820  7f8101ce stvx    v28,r1,r0 <-- POP
  c0000000000b9824  38000030 li      r0,48
  c0000000000b9828  7fa101ce stvx    v29,r1,r0
  ...
  c0000000000b984c  4bf6a06d bl      c0000000000238b8 # enable_kernel_altivec

This patch splits the non-altivec code into xor_vmx_glue.c which calls the
altivec functions in xor_vmx.c. By compiling xor_vmx_glue.c without
-maltivec we can guarantee that altivec instruction will not be executed
outside of the enable/disable block.

Signed-off-by: Matt Brown <matthew.brown.dev@gmail.com>
[mpe: Rework change log and include disassembly]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
arch/powerpc/lib/Makefile
arch/powerpc/lib/xor_vmx.c
arch/powerpc/lib/xor_vmx.h [new file with mode: 0644]
arch/powerpc/lib/xor_vmx_glue.c [new file with mode: 0644]