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authorLinus Torvalds <torvalds@linux-foundation.org>2012-05-04 07:50:50 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-05-04 07:50:50 -0700
commitf4622045455faaac958ca35a0cf313f3d6c14d8b (patch)
tree96455f6f8a1afca46d939e9937913eb21782214b /arch
parent0a6ba092d1c8c75ae0c0617ef7f4e6f5043af311 (diff)
parente419b4cc585680940bc42f8ca8a071d6023fb1bb (diff)
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/Kconfig2
-rw-r--r--arch/x86/include/asm/word-at-a-time.h33
2 files changed, 34 insertions, 1 deletions
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 1d14cc6b79a..c9866b0b77d 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 6fe6767b712..e58f03b206c 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 */