From: Mark Rutland <mark.rutland@arm.com>
To: Robin Murphy <robin.murphy@arm.com>
Cc: will@kernel.org, catalin.marinas@arm.com,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2] arm64: Rewrite __arch_clear_user()
Date: Wed, 26 May 2021 12:15:55 +0100 [thread overview]
Message-ID: <20210526111555.GB3806@C02TD0UTHF1T.local> (raw)
In-Reply-To: <ec0eb3452b572de993cac20093850d5b0c0ba003.1620993260.git.robin.murphy@arm.com>
On Fri, May 14, 2021 at 12:57:07PM +0100, Robin Murphy wrote:
> 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
Could we note the reason for the alignment in the commit message? IIUC
that's for consistency with the other routines.
Regardless, this looks good to me. I hand-executed this for `sz` in the
range 0 to 7 to make sure the logic and fixups were correct, and that
all looks good to me. FWIW:
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Mark.
> 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
>
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next prev parent reply other threads:[~2021-05-26 13:35 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 ` [PATCH v2] " Robin Murphy
2021-05-26 11:15 ` Mark Rutland [this message]
2021-05-27 13:24 ` Robin Murphy
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