linux-kernel - [PATCH 1/3] x86-32: Teach copy_from

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Date:   Thu,  1 Jun 2017 07:58:41 +0100
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     linux-kernel@...r.kernel.org
Cc:     x86@...nel.org, intel-gfx@...ts.freedesktop.org,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH 1/3] x86-32: Teach copy_from_user to unroll .size=6/8

Two exception handling register moves are faster to inline than a call
to __copy_user_ll(). We already apply the conversion for a get_user()
call, so for symmetry we should also apply the optimisation to
copy_from_user.

Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
---
 arch/x86/include/asm/uaccess_32.h | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/uaccess_32.h b/arch/x86/include/asm/uaccess_32.h
index aeda9bb8af50..44d17d1ab07c 100644
--- a/arch/x86/include/asm/uaccess_32.h
+++ b/arch/x86/include/asm/uaccess_32.h
@@ -23,30 +23,47 @@ static __always_inline unsigned long
 raw_copy_from_user(void *to, const void __user *from, unsigned long n)
 {
 	if (__builtin_constant_p(n)) {
-		unsigned long ret;
+		unsigned long ret = 0;
 
 		switch (n) {
 		case 1:
-			ret = 0;
 			__uaccess_begin();
 			__get_user_asm_nozero(*(u8 *)to, from, ret,
 					      "b", "b", "=q", 1);
 			__uaccess_end();
 			return ret;
 		case 2:
-			ret = 0;
 			__uaccess_begin();
 			__get_user_asm_nozero(*(u16 *)to, from, ret,
 					      "w", "w", "=r", 2);
 			__uaccess_end();
 			return ret;
 		case 4:
-			ret = 0;
 			__uaccess_begin();
 			__get_user_asm_nozero(*(u32 *)to, from, ret,
 					      "l", "k", "=r", 4);
 			__uaccess_end();
 			return ret;
+		case 6:
+			__uaccess_begin();
+			__get_user_asm_nozero(*(u32 *)to, from, ret,
+					      "l", "k", "=r", 6);
+			if (likely(!ret))
+				__get_user_asm_nozero(*(u16 *)(4 + (char *)to),
+						      (u16 __user *)(4 + (char __user *)from),
+						      ret, "w", "w", "=r", 2);
+			__uaccess_end();
+			return ret;
+		case 8:
+			__uaccess_begin();
+			__get_user_asm_nozero(*(u32 *)to, from, ret,
+					      "l", "k", "=r", 8);
+			if (likely(!ret))
+				__get_user_asm_nozero(*(u32 *)(4 + (char *)to),
+						      (u32 __user *)(4 + (char __user *)from),
+						      ret, "l", "k", "=r", 4);
+			__uaccess_end();
+			return ret;
 		}
 	}
 	return __copy_user_ll(to, (__force const void *)from, n);
-- 
2.11.0