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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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e419b4cc58
It turns out that there are more cases than CONFIG_DEBUG_PAGEALLOC that can have holes in the kernel address space: it seems to happen easily with Xen, and it looks like the AMD gart64 code will also punch holes dynamically. Actually hitting that case is still very unlikely, so just do the access, and take an exception and fix it up for the very unlikely case of it being a page-crosser with no next page. And hey, this abstraction might even help other architectures that have other issues with unaligned word accesses than the possible missing next page. IOW, this could do the byte order magic too. Peter Anvin fixed a thinko in the shifting for the exception case. Reported-and-tested-by: Jana Saout <jana@saout.de> Cc: Peter Anvin <hpa@zytor.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
80 lines
1.9 KiB
C
80 lines
1.9 KiB
C
#ifndef _ASM_WORD_AT_A_TIME_H
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#define _ASM_WORD_AT_A_TIME_H
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/*
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* This is largely generic for little-endian machines, but the
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* optimal byte mask counting is probably going to be something
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* that is architecture-specific. If you have a reliably fast
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* bit count instruction, that might be better than the multiply
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* and shift, for example.
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*/
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#ifdef CONFIG_64BIT
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/*
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* Jan Achrenius on G+: microoptimized version of
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* the simpler "(mask & ONEBYTES) * ONEBYTES >> 56"
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* that works for the bytemasks without having to
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* mask them first.
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*/
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static inline long count_masked_bytes(unsigned long mask)
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{
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return mask*0x0001020304050608ul >> 56;
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}
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#else /* 32-bit case */
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/* Carl Chatfield / Jan Achrenius G+ version for 32-bit */
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static inline long count_masked_bytes(long mask)
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{
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/* (000000 0000ff 00ffff ffffff) -> ( 1 1 2 3 ) */
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long a = (0x0ff0001+mask) >> 23;
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/* Fix the 1 for 00 case */
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return a & mask;
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}
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#endif
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#define REPEAT_BYTE(x) ((~0ul / 0xff) * (x))
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/* Return the high bit set in the first byte that is a zero */
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static inline unsigned long has_zero(unsigned long a)
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{
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return ((a - REPEAT_BYTE(0x01)) & ~a) & REPEAT_BYTE(0x80);
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}
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/*
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* Load an unaligned word from kernel space.
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*
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* In the (very unlikely) case of the word being a page-crosser
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* and the next page not being mapped, take the exception and
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* return zeroes in the non-existing part.
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*/
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static inline unsigned long load_unaligned_zeropad(const void *addr)
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{
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unsigned long ret, dummy;
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asm(
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"1:\tmov %2,%0\n"
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"2:\n"
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".section .fixup,\"ax\"\n"
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"3:\t"
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"lea %2,%1\n\t"
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"and %3,%1\n\t"
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"mov (%1),%0\n\t"
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"leal %2,%%ecx\n\t"
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"andl %4,%%ecx\n\t"
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"shll $3,%%ecx\n\t"
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"shr %%cl,%0\n\t"
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"jmp 2b\n"
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".previous\n"
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_ASM_EXTABLE(1b, 3b)
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:"=&r" (ret),"=&c" (dummy)
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:"m" (*(unsigned long *)addr),
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"i" (-sizeof(unsigned long)),
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"i" (sizeof(unsigned long)-1));
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return ret;
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}
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#endif /* _ASM_WORD_AT_A_TIME_H */
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