linux-kernel - [PATCH 2/3] x86-32: Expand static copy_to

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Date:   Thu,  1 Jun 2017 07:58:42 +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 2/3] x86-32: Expand static copy_to_user()

For known compile-time fixed sizes, teach x86-32 copy_to_user() to
convert them to the simpler put_user and inline it similar to the
optimisation applied to copy_from_user() and already used by x86-64.

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 | 48 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/arch/x86/include/asm/uaccess_32.h b/arch/x86/include/asm/uaccess_32.h
index 44d17d1ab07c..a02aa9db34ed 100644
--- a/arch/x86/include/asm/uaccess_32.h
+++ b/arch/x86/include/asm/uaccess_32.h
@@ -16,6 +16,54 @@ unsigned long __must_check __copy_from_user_ll_nocache_nozero
 static __always_inline unsigned long __must_check
 raw_copy_to_user(void __user *to, const void *from, unsigned long n)
 {
+	if (__builtin_constant_p(n)) {
+		unsigned long ret = 0;
+
+		switch (n) {
+		case 1:
+			__uaccess_begin();
+			__put_user_asm(*(u8 *)from, to, ret,
+					"b", "b", "iq", 1);
+			__uaccess_end();
+			return ret;
+		case 2:
+			__uaccess_begin();
+			__put_user_asm(*(u16 *)from, to, ret,
+					"w", "w", "ir", 2);
+			__uaccess_end();
+			return ret;
+		case 4:
+			__uaccess_begin();
+			__put_user_asm(*(u32 *)from, to, ret,
+					"l", "k", "ir", 4);
+			__uaccess_end();
+			return ret;
+		case 6:
+			__uaccess_begin();
+			__put_user_asm(*(u32 *)from, to, ret,
+					"l", "k", "ir", 4);
+			if (likely(!ret)) {
+				asm("":::"memory");
+				__put_user_asm(*(u16 *)(4 + (char *)from),
+						(u16 __user *)(4 + (char __user *)to),
+						ret, "w", "w", "ir", 2);
+			}
+			__uaccess_end();
+			return ret;
+		case 8:
+			__uaccess_begin();
+			__put_user_asm(*(u32 *)from, to, ret,
+					"l", "k", "ir", 4);
+			if (likely(!ret)) {
+				asm("":::"memory");
+				__put_user_asm(*(u32 *)(4 + (char *)from),
+						(u32 __user *)(4 + (char __user *)to),
+						ret, "l", "k", "ir", 4);
+			}
+			__uaccess_end();
+			return ret;
+		}
+	}
 	return __copy_user_ll((__force void *)to, from, n);
 }
 
-- 
2.11.0