linux-kernel - [tip: x86/asm] x86/math64: Provide a sane mul_u64_u32_div() implementation for x86

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Message-ID: <156749952104.13294.1046109089775898437.tip-bot2@tip-bot2>
Date:   Tue, 03 Sep 2019 08:32:01 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
Subject: [tip: x86/asm] x86/math64: Provide a sane mul_u64_u32_div()
 implementation for x86_64

The following commit has been merged into the x86/asm branch of tip:

Commit-ID:     db4e919d9a119b7c54eb5e5ac9bee5d3eb4cb859
Gitweb:        https://git.kernel.org/tip/db4e919d9a119b7c54eb5e5ac9bee5d3eb4cb859
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Wed, 28 Aug 2019 17:39:46 +02:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Tue, 03 Sep 2019 08:56:14 +02:00

x86/math64: Provide a sane mul_u64_u32_div() implementation for x86_64

On x86_64 we can do a u64 * u64 -> u128 widening multiply followed by
a u128 / u64 -> u64 division to implement a sane version of
mul_u64_u32_div().

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/include/asm/div64.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/x86/include/asm/div64.h b/arch/x86/include/asm/div64.h
index 20a4615..9b8cb50 100644
--- a/arch/x86/include/asm/div64.h
+++ b/arch/x86/include/asm/div64.h
@@ -73,6 +73,19 @@ static inline u64 mul_u32_u32(u32 a, u32 b)
 
 #else
 # include <asm-generic/div64.h>
+
+static inline u64 mul_u64_u32_div(u64 a, u32 mul, u32 div)
+{
+	u64 q;
+
+	asm ("mulq %2; divq %3" : "=a" (q)
+				: "a" (a), "rm" ((u64)mul), "rm" ((u64)div)
+				: "rdx");
+
+	return q;
+}
+#define mul_u64_u32_div	mul_u64_u32_div
+
 #endif /* CONFIG_X86_32 */
 
 #endif /* _ASM_X86_DIV64_H */