diff mbox series

[1/9] mm/maccess: fix unaligned copy_{from,to}_kernel_nofault

Message ID 20201030154919.1246645-1-arnd@kernel.org (mailing list archive)
State New, archived
Headers show
Series ARM: remove set_fs callers and implementation | expand

Commit Message

Arnd Bergmann Oct. 30, 2020, 3:49 p.m. UTC 
From: Arnd Bergmann <arnd@arndb.de>

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>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 mm/maccess.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

Comments

Linus Walleij Nov. 6, 2020, 8:57 a.m. UTC | #1 
On Fri, Oct 30, 2020 at 4:49 PM Arnd Bergmann <arnd@kernel.org> wrote:

> From: Arnd Bergmann <arnd@arndb.de>
>
> 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>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij
diff mbox series

Patch

diff --git a/mm/maccess.c b/mm/maccess.c
index 3bd70405f2d8..d3f1a1f0b1c1 100644
--- 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)
 {
+	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;