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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2012-05-04 07:50:50 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-05-04 07:50:50 -0700 |
| commit | f4622045455faaac958ca35a0cf313f3d6c14d8b (patch) | |
| tree | 96455f6f8a1afca46d939e9937913eb21782214b /arch | |
| parent | 0a6ba092d1c8c75ae0c0617ef7f4e6f5043af311 (diff) | |
| parent | e419b4cc585680940bc42f8ca8a071d6023fb1bb (diff) | |
| download | linux-f4622045455faaac958ca35a0cf313f3d6c14d8b.tar.gz linux-f4622045455faaac958ca35a0cf313f3d6c14d8b.tar.bz2 linux-f4622045455faaac958ca35a0cf313f3d6c14d8b.zip | |
Merge branch 'fix-unmapped-word-at-a-time'
Jana Saout confirmed that this fixes the page faults he saw.
His problem was triggered by ocfs2 and autofs symlink lookups, where the
symlink allocation was at the end of a page. But the deeper reason
seems to be the use of Xen-PV, which is what then causes him to have all
these unmapped pages, which is what then makes it a problem when the
unaligned word-at-a-time code fetches data past the end of a page.
* fix-unmapped-word-at-a-time:
vfs: make word-at-a-time accesses handle a non-existing page
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/Kconfig | 2 | ||||
| -rw-r--r-- | arch/x86/include/asm/word-at-a-time.h | 33 |
2 files changed, 34 insertions, 1 deletions
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 1d14cc6b79ad..c9866b0b77d8 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -81,7 +81,7 @@ config X86 select CLKEVT_I8253 select ARCH_HAVE_NMI_SAFE_CMPXCHG select GENERIC_IOMAP - select DCACHE_WORD_ACCESS if !DEBUG_PAGEALLOC + select DCACHE_WORD_ACCESS config INSTRUCTION_DECODER def_bool (KPROBES || PERF_EVENTS) diff --git a/arch/x86/include/asm/word-at-a-time.h b/arch/x86/include/asm/word-at-a-time.h index 6fe6767b7124..e58f03b206c3 100644 --- a/arch/x86/include/asm/word-at-a-time.h +++ b/arch/x86/include/asm/word-at-a-time.h @@ -43,4 +43,37 @@ static inline unsigned long has_zero(unsigned long a) return ((a - REPEAT_BYTE(0x01)) & ~a) & REPEAT_BYTE(0x80); } +/* + * Load an unaligned word from kernel space. + * + * In the (very unlikely) case of the word being a page-crosser + * and the next page not being mapped, take the exception and + * return zeroes in the non-existing part. + */ +static inline unsigned long load_unaligned_zeropad(const void *addr) +{ + unsigned long ret, dummy; + + asm( + "1:\tmov %2,%0\n" + "2:\n" + ".section .fixup,\"ax\"\n" + "3:\t" + "lea %2,%1\n\t" + "and %3,%1\n\t" + "mov (%1),%0\n\t" + "leal %2,%%ecx\n\t" + "andl %4,%%ecx\n\t" + "shll $3,%%ecx\n\t" + "shr %%cl,%0\n\t" + "jmp 2b\n" + ".previous\n" + _ASM_EXTABLE(1b, 3b) + :"=&r" (ret),"=&c" (dummy) + :"m" (*(unsigned long *)addr), + "i" (-sizeof(unsigned long)), + "i" (sizeof(unsigned long)-1)); + return ret; +} + #endif /* _ASM_WORD_AT_A_TIME_H */ |