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SubjectRe: [RFC PATCH v2 0/7] Pseudo-NMI for arm64 using ICC_PMR_EL1 (GICv3)
(Apologies for top posting)

I think there is a need to connect a few dots on this next week during Connect. Some other conversations have discussed alternative implementations elsewhere. I will assist.

--
Computer Architect | Sent from my 64-bit #ARM Powered phone

> On Sep 14, 2015, at 06:26, Daniel Thompson <daniel.thompson@linaro.org> wrote:
>
> This patchset provides a pseudo-NMI for arm64 kernels by reimplementing
> the irqflags macros to modify the GIC PMR (the priority mask register is
> 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
> exercised.
>
> The code works-for-me (tm) and is much 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. The alternatives runtime
> patching system is employed so systems with earlier GIC architectures
> are still bootable but will not benefit from NMI simulation.
>
> 2. Currently hardcoded to use ICC_PMR_EL1. Extra work might be needed
> on the alternatives system so we can peacefully coexist with ARMv8.1
> KVM support (when kernel will be running at EL2).
>
> 3. 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 can share the hacks (and DTs) I have been using to test with.
>
> 4. Testing for non regression on a GICv2 system will require this patch
> to avoid crashes during <SysRq-L>:
> http://article.gmane.org/gmane.linux.kernel/2037558
>
> v2:
>
> * 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
> King).
>
>
> Daniel Thompson (7):
> irqchip: gic-v3: Reset BPR during initialization
> arm64: Add support for on-demand backtrace of other CPUs
> 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
> arm64: irqflags: Automatically identify I bit mis-management
>
> arch/arm64/Kconfig | 15 ++++
> arch/arm64/include/asm/alternative.h | 1 +
> arch/arm64/include/asm/assembler.h | 56 ++++++++++++-
> arch/arm64/include/asm/hardirq.h | 2 +-
> arch/arm64/include/asm/irq.h | 3 +
> arch/arm64/include/asm/irqflags.h | 154 +++++++++++++++++++++++++++++++++--
> arch/arm64/include/asm/ptrace.h | 18 ++++
> arch/arm64/include/asm/smp.h | 2 +
> arch/arm64/kernel/alternative.c | 15 ++++
> arch/arm64/kernel/entry.S | 149 +++++++++++++++++++++++++++------
> arch/arm64/kernel/head.S | 35 ++++++++
> arch/arm64/kernel/setup.c | 13 +++
> arch/arm64/kernel/smp.c | 44 ++++++++++
> arch/arm64/mm/proc.S | 23 ++++++
> drivers/irqchip/irq-gic-v3.c | 117 +++++++++++++++++++++++++-
> include/linux/irqchip/arm-gic-v3.h | 10 +++
> include/linux/irqchip/arm-gic.h | 2 +-
> lib/nmi_backtrace.c | 8 +-
> 18 files changed, 629 insertions(+), 38 deletions(-)
>
> --
> 2.4.3
>
> _______________________________________________
> linaro-kernel mailing list
> linaro-kernel@lists.linaro.org
> https://lists.linaro.org/mailman/listinfo/linaro-kernel


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