linux-kernel - [PATCH v2 15/17] arm64: Add test_and_clear_flag and set

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Date:   Tue, 29 May 2018 13:11:19 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu
Cc:     Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Christoffer Dall <christoffer.dall@....com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Julien Grall <julien.grall@....com>,
        Mark Rutland <mark.rutland@....com>
Subject: [PATCH v2 15/17] arm64: Add test_and_clear_flag and set_flag atomic assembler primitives

As we're about to need to atomically manipulate some thread
flags from entry.S, let's introduce two atomic primitives
(test_and_clear_flag and set_flag) for that purpose.

We provide two implementations: one using the traditional
LL/SC instructions, and one using the ARMv8.1 atomics.

Signed-off-by: Marc Zyngier <marc.zyngier@....com>
---
 arch/arm64/include/asm/assembler.h | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index 0bcc98dbba56..d3612ad8035e 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -26,6 +26,7 @@
 #include <asm/asm-offsets.h>
 #include <asm/cpufeature.h>
 #include <asm/debug-monitors.h>
+#include <asm/lse.h>
 #include <asm/page.h>
 #include <asm/pgtable-hwdef.h>
 #include <asm/ptrace.h>
@@ -701,4 +702,40 @@ USER(\label, ic	ivau, \tmp2)			// invalidate I line PoU
 .Lyield_out_\@ :
 	.endm
 
+/*
+ * test_and_clear_flag:
+ *
+ * res: register containing the result (0 or 1 << bitnum)
+ * addr: address of the word to be manipulated
+ * bitnum: number of the bit in that word
+ * wtmp: temporary register, must be a 32bit reg
+ */
+	.macro test_and_clear_flag, res, addr, bitnum, wtmp
+alt_lse "  prfm	 pstl1strm, [\addr]",		"nop"
+alt_lse "8:ldxr  \res, [\addr]",		"ldr	 \res, [\addr]"
+	   tbz	 \res, #\bitnum, 9f
+alt_lse "  bic	 \res, \res, #(1 << \bitnum)",	"mov	 \res, #(1 << \bitnum)"
+alt_lse "  stlxr \wtmp, \res, [\addr]",		"ldclral \res, \res, [\addr]"
+alt_lse "  cbnz	 \wtmp, 8b",			"nop"
+alt_lse "  dmb   ish",				"nop"
+alt_lse "  orr	 \res, \res, #(1 << \bitnum)",	"nop"
+9:
+	.endm
+
+/*
+ * set_flag:
+ *
+ * addr: address of the word to be manipulated
+ * bitnum: number of the bit in that word
+ * tmp: temporary register
+ * wtmp: temporary register, must be a 32bit reg
+ */
+	.macro set_flag, addr, bitnum, tmp, wtmp
+alt_lse "  prfm	pstl1strm, [\addr]",		"mov   \tmp, #(1 << \bitnum)"
+alt_lse "8:ldxr \tmp, [\addr]", 		"stset \tmp, [\addr]"
+alt_lse "  orr	\tmp, \tmp, #(1 << \bitnum)",	"nop"
+alt_lse "  stxr \wtmp, \tmp, [\addr]",		"nop"
+alt_lse "  cbnz	\wtmp, 8b",			"nop"
+	.endm
+
 #endif	/* __ASM_ASSEMBLER_H */
-- 
2.14.2