Commit 0fe4f4ef authored by Nick Terrell's avatar Nick Terrell Committed by Ingo Molnar

x86: Bump ZO_z_extra_bytes margin for zstd

Bump the ZO_z_extra_bytes margin for zstd.

Zstd needs 3 bytes per 128 KB, and has a 22 byte fixed overhead.
Zstd needs to maintain 128 KB of space at all times, since that is
the maximum block size. See the comments regarding in-place
decompression added in lib/decompress_unzstd.c for details.

The existing code is written so that all the compression algorithms use
the same ZO_z_extra_bytes. It is taken to be the maximum of the growth
rate plus the maximum fixed overhead. The comments just above this diff
state that:
Signed-off-by: default avatarNick Terrell <terrelln@fb.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Tested-by: default avatarSedat Dilek <sedat.dilek@gmail.com>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20200730190841.2071656-6-nickrterrell@gmail.com
parent a30d8a39
...@@ -539,8 +539,14 @@ pref_address: .quad LOAD_PHYSICAL_ADDR # preferred load addr ...@@ -539,8 +539,14 @@ pref_address: .quad LOAD_PHYSICAL_ADDR # preferred load addr
# the size-dependent part now grows so fast. # the size-dependent part now grows so fast.
# #
# extra_bytes = (uncompressed_size >> 8) + 65536 # extra_bytes = (uncompressed_size >> 8) + 65536
#
# ZSTD compressed data grows by at most 3 bytes per 128K, and only has a 22
# byte fixed overhead but has a maximum block size of 128K, so it needs a
# larger margin.
#
# extra_bytes = (uncompressed_size >> 8) + 131072
#define ZO_z_extra_bytes ((ZO_z_output_len >> 8) + 65536) #define ZO_z_extra_bytes ((ZO_z_output_len >> 8) + 131072)
#if ZO_z_output_len > ZO_z_input_len #if ZO_z_output_len > ZO_z_input_len
# define ZO_z_extract_offset (ZO_z_output_len + ZO_z_extra_bytes - \ # define ZO_z_extract_offset (ZO_z_output_len + ZO_z_extra_bytes - \
ZO_z_input_len) ZO_z_input_len)
......
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