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Subject[RFC PATCH v3 0/7] Pseudo-NMI for arm64 using ICC_PMR_EL1 (GICv3)
This patchset provides a pseudo-NMI for arm64 kernels by reimplementing
the irqflags macros to modify the GIC PMR (the priority mask register
accessible as a system register on GICv3 and later) rather than the
PSR. The patchset includes an implementation of
arch_trigger_all_cpu_backtrace() for arm64 allowing the new code to be

The code works-for-me (tm) and is more "real" than the last time I
shared these patches. However there remain a couple of limitations
and caveats:

1. Requires GICv3+ hardware to be effective meaning it has mostly been
tested using FVP. The alternatives runtime patching system is
employed so systems with earlier GIC architectures are still
bootable but will not benefit from NMI simulation.

2. FVP needs a bit of hacking to be able to run <SysRq-L> from an ISR.
That's a shame because <SysRq-L> is a great way to observe an NMI
preempting an IRQ handler. Testers are welcome to ping me offline
and I will share the hacks I have been using to test with.


* Rebased on v4.8-rc2
* Restrict apply_alternatives_early() to consider only the
capabilities needed for the kernel to function correctly (Will
* Added a bunch of notrace qualifiers (Will Deacon)
* Used byte addressing to configure the interrupt priorities (Marc
* Fixed implementation of interrupts_enabled()
* Eliminated the over-zealous inclusion of <linux/irqchip/arm-gic-v3.h>.
* Pushed a few symbol defintions towards the end of the patch series.


* Removed the isb instructions. The PMR is self-synchronizing so
these are not needed (Dave Martin)
* Use alternative runtime patching to allow the same kernel binary
to boot systems with and without GICv3+ (Dave Martin).
* Added code to properly distinguish between NMI and normal IRQ and to
call into NMI handling code where needed.
* Replaced the IPI backtrace logic with a newer version (from Russell

Daniel Thompson (7):
irqchip: gic-v3: Reset BPR during initialization
arm64: Add support for on-demand backtrace of other CPUs
arm64: cpufeature: Allow early detect of specific features
arm64: alternative: Apply alternatives early in boot process
arm64: irqflags: Reorder the fiq & async macros
arm64: irqflags: Use ICC sysregs to implement IRQ masking
arm64: Implement IPI_CPU_BACKTRACE using pseudo-NMIs

arch/arm/include/asm/arch_gicv3.h | 6 ++
arch/arm64/Kconfig | 16 ++++
arch/arm64/include/asm/alternative.h | 1 +
arch/arm64/include/asm/arch_gicv3.h | 57 +++++++++++++
arch/arm64/include/asm/assembler.h | 55 +++++++++++-
arch/arm64/include/asm/hardirq.h | 2 +-
arch/arm64/include/asm/irq.h | 3 +
arch/arm64/include/asm/irqflags.h | 118 ++++++++++++++++++++++++--
arch/arm64/include/asm/ptrace.h | 23 +++++
arch/arm64/include/asm/smp.h | 2 +
arch/arm64/kernel/alternative.c | 36 +++++++-
arch/arm64/kernel/cpufeature.c | 92 +++++++++++---------
arch/arm64/kernel/entry.S | 151 +++++++++++++++++++++++++++------
arch/arm64/kernel/head.S | 35 ++++++++
arch/arm64/kernel/smp.c | 68 ++++++++++++++-
arch/arm64/mm/proc.S | 23 +++++
drivers/irqchip/irq-gic-v3.c | 72 ++++++++++++++++
include/linux/irqchip/arm-gic-common.h | 8 ++
include/linux/irqchip/arm-gic.h | 5 --
lib/nmi_backtrace.c | 9 +-
20 files changed, 697 insertions(+), 85 deletions(-)


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