[PATCH v2 0/5] MIPS: Add per-cpu IRQ stack

From: Matt Redfearn
Date: Tue Dec 13 2016 - 05:59:17 EST

This series adds a separate stack for each CPU wihin the system to use
when handling IRQs. Previously IRQs were handled on the kernel stack of
the current task. If that task was deep down a call stack at the point
of the interrupt, and handling the interrupt required a deep IRQ stack,
then there was a likelihood of stack overflow. Since the kernel stack
is in normal unmapped memory, overflowing it can lead to silent
corruption of other kernel data, with weird and wonderful results.

Before this patch series, ftracing the maximum stack size of a v4.9
kernel running on a Ci40 board gave:

And with this series:

Handling interrupts on a separate stack reduces the maximum kernel stack
usage in this configuration by ~900 bytes.

Since do_IRQ is now invoked on a separate stack, we select
HAVE_IRQ_EXIT_ON_IRQ_STACK so that softirqs will also be executed on the
irq stack rather than attempting to switch with do_softirq_own_stack().

This series has been tested on MIPS Boston, Malta and SEAD3 platforms,
Pistachio on the Creator Ci40 board and Cavium Octeon III.

Changes in v2:
Drop .set reorder/noreorder when updating $28

Matt Redfearn (5):
MIPS: Introduce irq_stack
MIPS: Stack unwinding while on IRQ stack
MIPS: Only change $28 to thread_info if coming from user mode
MIPS: Switch to the irq_stack in interrupts

arch/mips/Kconfig | 1 +
arch/mips/include/asm/irq.h | 12 ++++++
arch/mips/include/asm/stackframe.h | 8 ++++
arch/mips/kernel/asm-offsets.c | 1 +
arch/mips/kernel/genex.S | 81 +++++++++++++++++++++++++++++++++++---
arch/mips/kernel/irq.c | 11 ++++++
arch/mips/kernel/process.c | 15 ++++++-
7 files changed, 123 insertions(+), 6 deletions(-)