[PATCH] x86: Enable fast 32-bit put_user_64 for copy_to_user

From: Chris Wilson
Date: Wed Apr 15 2015 - 06:09:39 EST

For fixed sized copies, copy_to_user() will utilize __put_user_size
fastpaths. However, it is missing the translation for 64bit copies on
x86/32. Testing on a Pinetrail Atom, the 64 bit put_user fastpath is
substantially faster than the generic copy_to_user() fallback.

Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
CC: linux-kernel@xxxxxxxxxxxxxxx
arch/x86/include/asm/uaccess_32.h | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/arch/x86/include/asm/uaccess_32.h b/arch/x86/include/asm/uaccess_32.h
index 3c03a5de64d3..0ed5504c6060 100644
--- a/arch/x86/include/asm/uaccess_32.h
+++ b/arch/x86/include/asm/uaccess_32.h
@@ -59,6 +59,10 @@ __copy_to_user_inatomic(void __user *to, const void *from, unsigned long n)
__put_user_size(*(u32 *)from, (u32 __user *)to,
4, ret, 4);
return ret;
+ case 8:
+ __put_user_size(*(u64 *)from, (u64 __user *)to,
+ 8, ret, 8);
+ return ret;
return __copy_to_user_ll(to, from, n);

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