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 50ae5286f59b5096c13ece1dd6dce191bdb0dd1a..359a3b85c8b37b9e864a3671ae9c7365db365855 100644 (file)
--- 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 4e0d318b67c6c92ebadb76ce3b140f33ec49d697..de8a60363c8597769d0d3b5d8bbe28208c724bdd 100644 (file)
--- 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
        @