linux-kernel - [PATCH] x86/uaccess: small optimization in unsafe_copy_to

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Date:   Fri, 16 Apr 2021 12:24:13 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH] x86/uaccess: small optimization in unsafe_copy_to_user()

From: Eric Dumazet <edumazet@...gle.com>

We have to loop only to copy u64 values.
After this first loop, we copy at most one u32, one u16 and one byte.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 arch/x86/include/asm/uaccess.h | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index c9fa7be3df82ddb9495961b3e2f22b1ac07edafa..ddb19bb8c86786d78407dcfb59623943ccbce8a8 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -517,15 +517,23 @@ do {										\
 		len -= sizeof(type);						\
 	}
 
+#define unsafe_copy_elem(dst, src, len, type, label)				\
+	if (len >= sizeof(type)) {						\
+		unsafe_put_user(*(type *)(src),(type __user *)(dst),label);	\
+		dst += sizeof(type);						\
+		src += sizeof(type);						\
+		len -= sizeof(type);						\
+	}
+
 #define unsafe_copy_to_user(_dst,_src,_len,label)			\
 do {									\
 	char __user *__ucu_dst = (_dst);				\
 	const char *__ucu_src = (_src);					\
 	size_t __ucu_len = (_len);					\
 	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u64, label);	\
-	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u32, label);	\
-	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u16, label);	\
-	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u8, label);	\
+	unsafe_copy_elem(__ucu_dst, __ucu_src, __ucu_len, u32, label);	\
+	unsafe_copy_elem(__ucu_dst, __ucu_src, __ucu_len, u16, label);	\
+	unsafe_copy_elem(__ucu_dst, __ucu_src, __ucu_len, u8, label);	\
 } while (0)
 
 #define HAVE_GET_KERNEL_NOFAULT
-- 
2.31.1.368.gbe11c130af-goog