From: Ard Biesheuvel <ardb@kernel.org>
To: linux-arm-kernel@lists.infradead.org, linux@armlinux.org.uk
Cc: arnd@arndb.de, linus.walleij@linaro.org,
Ard Biesheuvel <ardb@kernel.org>
Subject: [PATCH 4/6] ARM: spectre-bhb: use local DSB and elide ISB in loop8 sequence
Date: Mon, 28 Mar 2022 15:47:12 +0200 [thread overview]
Message-ID: <20220328134714.205342-5-ardb@kernel.org> (raw)
In-Reply-To: <20220328134714.205342-1-ardb@kernel.org>
The loop8 mitigation for Spectre-BHB only requires a CPU local DSB
rather than a systemwide one, which is much more costly. And by the same
reasoning as why it is justified to omit the ISB after BPIALL, we can
also elide the ISB and rely on the exception return for the context
synchronization.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/arm/kernel/entry-armv.S | 5 +++--
arch/arm/kernel/entry-common.S | 2 +-
2 files changed, 4 insertions(+), 3 deletions(-)
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index a5725e82addc..3a62ee790b5e 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -1049,8 +1049,9 @@ vector_bhb_loop8_\name:
3: W(b) . + 4
subs r0, r0, #1
bne 3b
- dsb
- isb
+ dsb nsh
+ @ isb not needed due to "movs pc, lr" in the vector stub
+ @ which gives a "context synchronisation".
b 2b
ENDPROC(vector_bhb_loop8_\name)
.previous
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index dbc1913ee30b..96016a5ad72f 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -162,7 +162,7 @@ ENTRY(vector_bhb_loop8_swi)
1: b 2f
2: subs r8, r8, #1
bne 1b
- dsb
+ dsb nsh
isb
b 3f
ENDPROC(vector_bhb_loop8_swi)
--
2.30.2
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next prev parent reply other threads:[~2022-03-28 13:54 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-28 13:47 [PATCH 0/6] ARM: spectre-bhb fixes and tweaks Ard Biesheuvel
2022-03-28 13:47 ` [PATCH 1/6] ARM: spectre-bhb: enable for Cortex-A15 Ard Biesheuvel
2022-05-24 14:50 ` Jon Hunter
2022-05-24 15:21 ` Ard Biesheuvel
2022-05-24 16:06 ` Jon Hunter
2022-05-24 17:03 ` Russell King (Oracle)
2022-05-24 17:49 ` Jon Hunter
2022-05-25 7:09 ` Ard Biesheuvel
2022-05-25 10:48 ` Jon Hunter
2022-05-25 10:52 ` Ard Biesheuvel
2022-06-07 14:30 ` Jon Hunter
2022-06-07 14:32 ` Ard Biesheuvel
2022-06-07 14:35 ` Jon Hunter
2022-06-07 14:39 ` Ard Biesheuvel
2022-03-28 13:47 ` [PATCH 2/6] ARM: spectre-bhb: fix loop8 sequence for Thumb2 Ard Biesheuvel
2022-03-28 13:47 ` [PATCH 3/6] ARM: spectre-bhb: simplify BPIALL vector macro Ard Biesheuvel
2022-03-28 13:47 ` Ard Biesheuvel [this message]
2022-03-28 13:47 ` [PATCH 5/6] ARM: spectre-bhb: avoid cross-subsection jump using a numbered label Ard Biesheuvel
2022-03-31 14:07 ` Russell King (Oracle)
2022-03-31 16:22 ` Ard Biesheuvel
2022-03-28 13:47 ` [PATCH 6/6] ARM: spectre-bhb: rely on linker to emit cross-section literal loads Ard Biesheuvel
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