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ARM: 9115/1: mm/maccess: fix unaligned copy_{from,to}_kernel_nofault 

On machines such as ARMv5 that trap unaligned accesses, these
two functions can be slow when each access needs to be emulated,
or they might not work at all.

Change them so that each loop is only used when both the src
and dst pointers are naturally aligned.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
This commit is contained in:
Arnd Bergmann 2021-08-11 08:30:18 +01:00 committed by Russell King (Oracle)
parent b30d0289de
commit 2423de2e6f
1 changed files with 22 additions and 6 deletions
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28
mm/maccess.c
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@ -24,13 +24,21 @@ bool __weak copy_from_kernel_nofault_allowed(const void *unsafe_src,
long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
{
unsigned long align = 0;
if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
align = (unsigned long)dst | (unsigned long)src;
if (!copy_from_kernel_nofault_allowed(src, size))
return -ERANGE;
pagefault_disable();
copy_from_kernel_nofault_loop(dst, src, size, u64, Efault);
copy_from_kernel_nofault_loop(dst, src, size, u32, Efault);
copy_from_kernel_nofault_loop(dst, src, size, u16, Efault);
if (!(align & 7))
copy_from_kernel_nofault_loop(dst, src, size, u64, Efault);
if (!(align & 3))
copy_from_kernel_nofault_loop(dst, src, size, u32, Efault);
if (!(align & 1))
copy_from_kernel_nofault_loop(dst, src, size, u16, Efault);
copy_from_kernel_nofault_loop(dst, src, size, u8, Efault);
pagefault_enable();
return 0;
@ -50,10 +58,18 @@ EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);
long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
{
unsigned long align = 0;
if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
align = (unsigned long)dst | (unsigned long)src;
pagefault_disable();
copy_to_kernel_nofault_loop(dst, src, size, u64, Efault);
copy_to_kernel_nofault_loop(dst, src, size, u32, Efault);
copy_to_kernel_nofault_loop(dst, src, size, u16, Efault);
if (!(align & 7))
copy_to_kernel_nofault_loop(dst, src, size, u64, Efault);
if (!(align & 3))
copy_to_kernel_nofault_loop(dst, src, size, u32, Efault);
if (!(align & 1))
copy_to_kernel_nofault_loop(dst, src, size, u16, Efault);
copy_to_kernel_nofault_loop(dst, src, size, u8, Efault);
pagefault_enable();
return 0;