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From: Ard Biesheuvel <ardb@kernel.org>
To: linux@armlinux.org.uk
Cc: linux-arm-kernel@lists.infradead.org,
	Ard Biesheuvel <ardb@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Kees Cook <keescook@chromium.org>,
	Keith Packard <keithpac@amazon.com>,
	Linus Walleij <linus.walleij@linaro.org>
Subject: [PATCH 04/10] ARM: optimize indirect call to handle_arch_irq for v7 cores
Date: Tue, 21 Sep 2021 11:54:02 +0200	[thread overview]
Message-ID: <20210921095408.133210-5-ardb@kernel.org> (raw)
In-Reply-To: <20210921095408.133210-1-ardb@kernel.org>

The current irq_handler macro uses a literal load followed by an
explicit assignment of lr before an indirect call, both of which are
sub-optimal on recent ARM cores. Replace it by a mov_l call, which will
evaluate to a movw/movt pair on v7 cores, avoiding one of the two loads,
followed by a call to a newly introduced 'bl_m' macro, which will
evaluate to a blx instruction on cores that support it. (Setting lr
explicitly rather than via a bl or blx instruction confuses the return
address prediction that modern out-of-order cores use to speculatively
perform the function return.)

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm/kernel/entry-armv.S | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index a54b5044d406..21896f702447 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -38,14 +38,12 @@
  */
 	.macro	irq_handler
 #ifdef CONFIG_GENERIC_IRQ_MULTI_HANDLER
-	ldr	r1, =handle_arch_irq
+	mov_l	r1, handle_arch_irq
 	mov	r0, sp
-	badr	lr, 9997f
-	ldr	pc, [r1]
+	bl_m	[r1]
 #else
 	arch_irq_handler_default
 #endif
-9997:
 	.endm
 
 	.macro	pabt_helper
-- 
2.30.2


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  parent reply	other threads:[~2021-09-21  9:57 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-21  9:53 [PATCH 00/10] ARM: add support for IRQ stacks Ard Biesheuvel
2021-09-21  9:53 ` [PATCH 01/10] ARM: fix incorrect use of get_kernel_nofault() Ard Biesheuvel
2021-09-21 10:39   ` Arnd Bergmann
2021-09-21 14:02   ` Russell King (Oracle)
2021-09-21 14:33     ` Ard Biesheuvel
2021-09-21  9:54 ` [PATCH 02/10] ARM: remove some dead code Ard Biesheuvel
2021-09-21  9:54 ` [PATCH 03/10] ARM: assembler: introduce bl_r and bl_m macros Ard Biesheuvel
2021-09-21  9:54 ` Ard Biesheuvel [this message]
2021-09-21  9:54 ` [PATCH 05/10] ARM: unwind: support unwinding across multiple stacks Ard Biesheuvel
2021-09-21  9:54 ` [PATCH 06/10] ARM: export dump_mem() to other objects Ard Biesheuvel
2021-09-21  9:54 ` [PATCH 07/10] ARM: unwind: dump exception stack from calling frame Ard Biesheuvel
2021-09-21  9:54 ` [PATCH 08/10] ARM: implement IRQ stacks Ard Biesheuvel
2021-09-21  9:54 ` [PATCH 09/10] ARM: call_with_stack: add unwind support Ard Biesheuvel
2021-09-21  9:54 ` [PATCH 10/10] ARM: run softirqs on the per-CPU IRQ stack Ard Biesheuvel

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