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From: Robin Murphy <robin.murphy@arm.com>
To: will@kernel.org, catalin.marinas@arm.com
Cc: linux-arm-kernel@lists.infradead.org, yangyingliang@huawei.com,
	shenkai8@huawei.com
Subject: [PATCH 8/8] arm64: Rewrite __arch_clear_user()
Date: Tue, 11 May 2021 17:12:38 +0100	[thread overview]
Message-ID: <76a1700b0316b50fb5881da603f2daf3c81468f4.1620738177.git.robin.murphy@arm.com> (raw)
In-Reply-To: <cover.1620738177.git.robin.murphy@arm.com>

Now that we're always using STTR variants rather than abstracting two
different addressing modes, the user_ldst macro here is frankly more
obfuscating than helpful. Rewrite __arch_clear_user() with regular
USER() annotations so that it's clearer what's going on, and take the
opportunity to minimise the branchiness in the most common paths, which
also allows the exception fixup to return a more accurate result.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 arch/arm64/lib/clear_user.S | 42 +++++++++++++++++++------------------
 1 file changed, 22 insertions(+), 20 deletions(-)

diff --git a/arch/arm64/lib/clear_user.S b/arch/arm64/lib/clear_user.S
index af9afcbec92c..1005345b4066 100644
--- a/arch/arm64/lib/clear_user.S
+++ b/arch/arm64/lib/clear_user.S
@@ -1,12 +1,9 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 /*
- * Based on arch/arm/lib/clear_user.S
- *
- * Copyright (C) 2012 ARM Ltd.
+ * Copyright (C) 2021 Arm Ltd.
  */
-#include <linux/linkage.h>
 
-#include <asm/asm-uaccess.h>
+#include <linux/linkage.h>
 #include <asm/assembler.h>
 
 	.text
@@ -19,25 +16,30 @@
  *
  * Alignment fixed up by hardware.
  */
+	.p2align 4
 SYM_FUNC_START(__arch_clear_user)
-	mov	x2, x1			// save the size for fixup return
+	add	x2, x0, x1
 	subs	x1, x1, #8
 	b.mi	2f
 1:
-user_ldst 9f, sttr, xzr, x0, 8
+USER(9f, sttr	xzr, [x0])
+	add	x0, x0, #8
 	subs	x1, x1, #8
-	b.pl	1b
-2:	adds	x1, x1, #4
-	b.mi	3f
-user_ldst 9f, sttr, wzr, x0, 4
-	sub	x1, x1, #4
-3:	adds	x1, x1, #2
-	b.mi	4f
-user_ldst 9f, sttrh, wzr, x0, 2
-	sub	x1, x1, #2
-4:	adds	x1, x1, #1
-	b.mi	5f
-user_ldst 9f, sttrb, wzr, x0, 0
+	b.hi	1b
+USER(9f, sttr	xzr, [x2, #-8])
+	mov	x0, #0
+	ret
+
+2:	tbz	x1, #2, 3f
+USER(9f, sttr	wzr, [x0])
+USER(9f, sttr	wzr, [x2, #-4])
+	mov	x0, #0
+	ret
+
+3:	tbz	x1, #1, 4f
+USER(9f, sttrh	wzr, [x0])
+4:	tbz	x1, #0, 5f
+USER(9f, sttrb	wzr, [x2, #-1])
 5:	mov	x0, #0
 	ret
 SYM_FUNC_END(__arch_clear_user)
@@ -45,6 +47,6 @@ EXPORT_SYMBOL(__arch_clear_user)
 
 	.section .fixup,"ax"
 	.align	2
-9:	mov	x0, x2			// return the original size
+9:	sub	x0, x2, x0
 	ret
 	.previous
-- 
2.21.0.dirty


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  parent reply	other threads:[~2021-05-11 16:22 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-11 16:12 [PATCH 0/8] arm64: String function updates Robin Murphy
2021-05-11 16:12 ` [PATCH 1/8] arm64: Import latest version of Cortex Strings' memcmp Robin Murphy
2021-05-12 13:28   ` Mark Rutland
2021-05-12 13:38     ` Robin Murphy
2021-05-12 14:51       ` Szabolcs Nagy
2021-05-26 10:17         ` Mark Rutland
2021-05-11 16:12 ` [PATCH 2/8] arm64: Import latest version of Cortex Strings' strcmp Robin Murphy
2021-05-11 16:12 ` [PATCH 3/8] arm64: Import updated version of Cortex Strings' strlen Robin Murphy
2021-05-11 16:12 ` [PATCH 4/8] arm64: Import latest version of Cortex Strings' strncmp Robin Murphy
2021-05-11 16:12 ` [PATCH 5/8] arm64: Add assembly annotations for weak-PI-alias madness Robin Murphy
2021-05-11 16:12 ` [PATCH 6/8] arm64: Import latest memcpy()/memmove() implementation Robin Murphy
2021-05-11 16:12 ` [PATCH 7/8] arm64: Better optimised memchr() Robin Murphy
2021-05-14 14:55   ` Catalin Marinas
2021-05-14 18:38     ` Robin Murphy
2021-05-11 16:12 ` Robin Murphy [this message]
2021-05-12 10:48   ` [PATCH 8/8] arm64: Rewrite __arch_clear_user() Mark Rutland
2021-05-12 11:31     ` Robin Murphy
2021-05-12 13:06       ` Mark Rutland
2021-05-12 13:51         ` Robin Murphy
2021-05-14 11:57   ` [PATCH v2] " Robin Murphy
2021-05-26 11:15     ` Mark Rutland
2021-05-27 13:24       ` Robin Murphy

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