diff options
| author | Gao Xiang | 2020-12-15 20:44:03 -0800 |
|---|---|---|
| committer | Linus Torvalds | 2020-12-15 22:46:16 -0800 |
| commit | 89b158635ad79574bde8e94d45dad33f8cf09549 (patch) | |
| tree | b4a18063a819fb6d1f60e9d495c524048deee158 /lib/lz4 | |
| parent | 506dfc9906e5cbf453bbcd5eb627689435583558 (diff) | |
lib/lz4: explicitly support in-place decompression
LZ4 final literal copy could be overlapped when doing
in-place decompression, so it's unsafe to just use memcpy()
on an optimized memcpy approach but memmove() instead.
Upstream LZ4 has updated this years ago [1] (and the impact
is non-sensible [2] plus only a few bytes remain), this commit
just synchronizes LZ4 upstream code to the kernel side as well.
It can be observed as EROFS in-place decompression failure
on specific files when X86_FEATURE_ERMS is unsupported,
memcpy() optimization of commit 59daa706fbec ("x86, mem:
Optimize memcpy by avoiding memory false dependece") will
be enabled then.
Currently most modern x86-CPUs support ERMS, these CPUs just
use "rep movsb" approach so no problem at all. However, it can
still be verified with forcely disabling ERMS feature...
arch/x86/lib/memcpy_64.S:
ALTERNATIVE_2 "jmp memcpy_orig", "", X86_FEATURE_REP_GOOD, \
- "jmp memcpy_erms", X86_FEATURE_ERMS
+ "jmp memcpy_orig", X86_FEATURE_ERMS
We didn't observe any strange on arm64/arm/x86 platform before
since most memcpy() would behave in an increasing address order
("copy upwards" [3]) and it's the correct order of in-place
decompression but it really needs an update to memmove() for sure
considering it's an undefined behavior according to the standard
and some unique optimization already exists in the kernel.
[1] https://github.com/lz4/lz4/commit/33cb8518ac385835cc17be9a770b27b40cd0e15b
[2] https://github.com/lz4/lz4/pull/717#issuecomment-497818921
[3] https://sourceware.org/bugzilla/show_bug.cgi?id=12518
Link: https://lkml.kernel.org/r/20201122030749.2698994-1-hsiangkao@redhat.com
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
Reviewed-by: Nick Terrell <terrelln@fb.com>
Cc: Yann Collet <yann.collet.73@gmail.com>
Cc: Miao Xie <miaoxie@huawei.com>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Li Guifu <bluce.liguifu@huawei.com>
Cc: Guo Xuenan <guoxuenan@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib/lz4')
| -rw-r--r-- | lib/lz4/lz4_decompress.c | 6 | ||||
| -rw-r--r-- | lib/lz4/lz4defs.h | 1 |
2 files changed, 6 insertions, 1 deletions
diff --git a/lib/lz4/lz4_decompress.c b/lib/lz4/lz4_decompress.c index 00cb0d0b73e1..8a7724a6ce2f 100644 --- a/lib/lz4/lz4_decompress.c +++ b/lib/lz4/lz4_decompress.c @@ -263,7 +263,11 @@ static FORCE_INLINE int LZ4_decompress_generic( } } - LZ4_memcpy(op, ip, length); + /* + * supports overlapping memory regions; only matters + * for in-place decompression scenarios + */ + LZ4_memmove(op, ip, length); ip += length; op += length; diff --git a/lib/lz4/lz4defs.h b/lib/lz4/lz4defs.h index c91dd96ef629..673bd206aa98 100644 --- a/lib/lz4/lz4defs.h +++ b/lib/lz4/lz4defs.h @@ -146,6 +146,7 @@ static FORCE_INLINE void LZ4_writeLE16(void *memPtr, U16 value) * environments. This is needed when decompressing the Linux Kernel, for example. */ #define LZ4_memcpy(dst, src, size) __builtin_memcpy(dst, src, size) +#define LZ4_memmove(dst, src, size) __builtin_memmove(dst, src, size) static FORCE_INLINE void LZ4_copy8(void *dst, const void *src) { |