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>

1 files changed, 20 insertions, 0 deletions

diff --git a/arch/powerpc/lib/xor_vmx.h b/arch/powerpc/lib/xor_vmx.h
new file mode 100644
index 000000000000..4746708451ae
--- /dev/null
+++ b/arch/powerpc/lib/xor_vmx.h
@@ -0,0 +1,20 @@
+/*
+ * Simple interface to link xor_vmx.c and xor_vmx_glue.c
+ *
+ * Separating these file ensures that no altivec instructions are run
+ * outside of the enable/disable altivec block.
+ */
+
+void __xor_altivec_2(unsigned long bytes, unsigned long *v1_in,
+			     unsigned long *v2_in);
+
+void __xor_altivec_3(unsigned long bytes, unsigned long *v1_in,
+			     unsigned long *v2_in, unsigned long *v3_in);
+
+void __xor_altivec_4(unsigned long bytes, unsigned long *v1_in,
+			     unsigned long *v2_in, unsigned long *v3_in,
+			     unsigned long *v4_in);
+
+void __xor_altivec_5(unsigned long bytes, unsigned long *v1_in,
+			     unsigned long *v2_in, unsigned long *v3_in,
+			     unsigned long *v4_in, unsigned long *v5_in);