From: Ard Biesheuvel <ardb@kernel.org>
Date: Thu, 2 Dec 2021 08:36:59 +0000 (+0100)
Subject: ARM: v7m: enable support for IRQ stacks
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=cafc0eab168917ec9c0cd47d530a40cd40eb2928;p=linux.git

ARM: v7m: enable support for IRQ stacks

Enable support for IRQ stacks on !MMU, and add the code to the IRQ entry
path to switch to the IRQ stack if not running from it already.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Tested-by: Marc Zyngier <maz@kernel.org>
Tested-by: Vladimir Murzin <vladimir.murzin@arm.com> # ARMv7M
---

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 50ae5286f59b5..359a3b85c8b37 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1158,7 +1158,6 @@ config CURRENT_POINTER_IN_TPIDRURO
 
 config IRQSTACKS
 	def_bool y
-	depends on MMU
 	select HAVE_IRQ_EXIT_ON_IRQ_STACK
 	select HAVE_SOFTIRQ_ON_OWN_STACK
 
diff --git a/arch/arm/kernel/entry-v7m.S b/arch/arm/kernel/entry-v7m.S
index 4e0d318b67c6c..de8a60363c859 100644
--- a/arch/arm/kernel/entry-v7m.S
+++ b/arch/arm/kernel/entry-v7m.S
@@ -40,11 +40,24 @@ __irq_entry:
 	@ Invoke the IRQ handler
 	@
 	mov	r0, sp
-	stmdb	sp!, {lr}
+	ldr_this_cpu sp, irq_stack_ptr, r1, r2
+
+	@
+	@ If we took the interrupt while running in the kernel, we may already
+	@ be using the IRQ stack, so revert to the original value in that case.
+	@
+	subs	r2, sp, r0		@ SP above bottom of IRQ stack?
+	rsbscs	r2, r2, #THREAD_SIZE	@ ... and below the top?
+	movcs	sp, r0
+
+	push	{r0, lr}		@ preserve LR and original SP
+
 	@ routine called with r0 = struct pt_regs *
 	bl	generic_handle_arch_irq
 
-	pop	{lr}
+	pop	{r0, lr}
+	mov	sp, r0
+
 	@
 	@ Check for any pending work if returning to user
 	@