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powerpc/32: Add warning on misaligned copy_page() or clear_page()

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copy_page() and clear_page() expect page aligned destination, and
use dcbz instruction to clear entire cache lines based on the
assumption that the destination is cache aligned.

As shown during analysis of a bug in BTRFS filesystem, a misaligned
copy_page() can create bugs that are difficult to locate (see Link).

Add an explicit WARNING when copy_page() or clear_page() are called
with misaligned destination.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=204371
Link: https://lore.kernel.org/r/c6cea38f90480268d439ca44a645647e260fff09.1565941808.git.christophe.leroy@c-s.fr
This commit is contained in:
Christophe Leroy
2019-08-16 07:52:20 +00:00
committed by Michael Ellerman
parent f204338f8e
commit 7ab0b7cb89
2 changed files with 9 additions and 0 deletions
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5
arch/powerpc/kernel/misc_32.S
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@@ -452,7 +452,12 @@ END_FTR_SECTION_IFSET(CPU_FTR_COHERENT_ICACHE)
stwu r9,16(r3)
_GLOBAL(copy_page)
rlwinm r5, r3, 0, L1_CACHE_BYTES - 1
addi r3,r3,-4
0: twnei r5, 0 /* WARN if r3 is not cache aligned */
EMIT_BUG_ENTRY 0b,__FILE__,__LINE__, BUGFLAG_WARNING
addi r4,r4,-4
li r5,4