linux-kernel - [PATCH] x86: Enable fast 32-bit put_user_64 for copy_to

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Date:	Wed, 15 Apr 2015 10:51:26 +0100
From:	Chris Wilson <chris@...is-wilson.co.uk>
To:	intel-gfx@...ts.freedesktop.org
Cc:	Chris Wilson <chris@...is-wilson.co.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] x86: Enable fast 32-bit put_user_64 for copy_to_user

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@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: x86@...nel.org
CC: linux-kernel@...r.kernel.org
---
 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);
-- 
2.1.4

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