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>

diff --git a/mm/maccess.c b/mm/maccess.c
index 3bd70405f2d848d15ee90897e7e267eb3de2ebda..d3f1a1f0b1c1acca131d05b82e9c87c45467f4f2 100644 (file)
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -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)
 {
 
 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();
        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;
        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)
 {
 
 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();
        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;
        copy_to_kernel_nofault_loop(dst, src, size, u8, Efault);
        pagefault_enable();
        return 0;