linux-arm-kernel.lists.infradead.org archive mirror
 help / color / mirror / Atom feed
From: Robin Murphy <robin.murphy@arm.com>
To: will@kernel.org, catalin.marinas@arm.com
Cc: linux-arm-kernel@lists.infradead.org, mark.rutland@arm.com
Subject: [PATCH v2] arm64: Rewrite __arch_clear_user()
Date: Fri, 14 May 2021 12:57:07 +0100	[thread overview]
Message-ID: <ec0eb3452b572de993cac20093850d5b0c0ba003.1620993260.git.robin.murphy@arm.com> (raw)
In-Reply-To: <76a1700b0316b50fb5881da603f2daf3c81468f4.1620738177.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, while
also allowing the exception fixup to return an accurate result.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---

v2: Tweak exception fixup to be exact

 arch/arm64/lib/clear_user.S | 44 ++++++++++++++++++++-----------------
 1 file changed, 24 insertions(+), 20 deletions(-)

diff --git a/arch/arm64/lib/clear_user.S b/arch/arm64/lib/clear_user.S
index af9afcbec92c..d30c03f6caed 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(8f, sttr	wzr, [x2, #-4])
+	mov	x0, #0
+	ret
+
+3:	tbz	x1, #1, 4f
+USER(9f, sttrh	wzr, [x0])
+4:	tbz	x1, #0, 5f
+USER(7f, sttrb	wzr, [x2, #-1])
 5:	mov	x0, #0
 	ret
 SYM_FUNC_END(__arch_clear_user)
@@ -45,6 +47,8 @@ EXPORT_SYMBOL(__arch_clear_user)
 
 	.section .fixup,"ax"
 	.align	2
-9:	mov	x0, x2			// return the original size
+7:	sub	x0, x2, #5	// Adjust for faulting on the final byte...
+8:	add	x0, x0, #4	// ...or the second word of the 4-7 byte case
+9:	sub	x0, x2, x0
 	ret
 	.previous
-- 
2.21.0.dirty


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  parent reply	other threads:[~2021-05-14 11:59 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 ` [PATCH 8/8] arm64: Rewrite __arch_clear_user() Robin Murphy
2021-05-12 10:48   ` 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   ` Robin Murphy [this message]
2021-05-26 11:15     ` [PATCH v2] " Mark Rutland
2021-05-27 13:24       ` Robin Murphy

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=ec0eb3452b572de993cac20093850d5b0c0ba003.1620993260.git.robin.murphy@arm.com \
    --to=robin.murphy@arm.com \
    --cc=catalin.marinas@arm.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=mark.rutland@arm.com \
    --cc=will@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).