[PATCH] arm64: kexec: Add machine_kexec_mask_interrupts to kexec path

[Mark Rutland]

Hi Sameer,

On Wed, Apr 18, 2018 at 08:19:36PM -0600, Sameer Goel wrote:
> In kdump code path SPIs at GIC level are explicitly cleared by
> calling machine_kexec_mask_interrupts. In case of kexec this
> functionality is delegated for most part to the device shutdown
> functions.
> Add machine_kexec_mask_interrupts to machine_shutdown path to
> ensure that the irqs are masked at the gic level.

I think that for kdump, the plan is to try to get irqchips to reset
things in their probe paths (e.g. as that's the sanest place to poke
APRn). Doing that would render machine_kexec_mask_interrupts() redundant
for kexec.

> Signed-off-by: Sameer Goel <sgoel at codeaurora.org>
> ---
> Porting code for masking irqs at gic from kdump shutdown to kexec path.
> 
> There was discussion about this functionality in [1].
> 
> [1] https://patchwork.kernel.org/patch/9817499/

I don't follow why this is a problem. Nate mentions corrupting the new
kernel -- has a problem been observed in practice?

The purgatory code is run with IRQs masked at the CPU, and the new
kernel will initialise the GIC before enabling interrupts at the CPU.
Once probed, the SMMU driver can handle spurious interrupts.

So AFAICT there is no problem today. Am I missing something?

When could an interrupt be taken that would be problematic?

Currently, I don't see that this is necessary. Given we'd like to remove
machine_kexec_mask_interrupts() for the kdump case, I'd prefer that we
don't mandate it in the usual kexec case.

Thanks,
Mark.

> 
>  arch/arm64/include/asm/kexec.h    | 6 ++++++
>  arch/arm64/kernel/machine_kexec.c | 2 +-
>  arch/arm64/kernel/process.c       | 2 ++
>  3 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
> index e17f052..f9ddb41 100644
> --- a/arch/arm64/include/asm/kexec.h
> +++ b/arch/arm64/include/asm/kexec.h
> @@ -93,6 +93,12 @@ static inline void crash_prepare_suspend(void) {}
>  static inline void crash_post_resume(void) {}
>  #endif
>  
> +#if defined(CONFIG_KEXEC)
> +extern void machine_kexec_mask_interrupts(void);
> +#else
> +static inline void machine_kexec_mask_interrupts(void) {}
> +#endif
> +
>  #endif /* __ASSEMBLY__ */
>  
>  #endif
> diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
> index f76ea92..b453180 100644
> --- a/arch/arm64/kernel/machine_kexec.c
> +++ b/arch/arm64/kernel/machine_kexec.c
> @@ -213,7 +213,7 @@ void machine_kexec(struct kimage *kimage)
>  	BUG(); /* Should never get here. */
>  }
>  
> -static void machine_kexec_mask_interrupts(void)
> +void machine_kexec_mask_interrupts(void)
>  {
>  	unsigned int i;
>  	struct irq_desc *desc;
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index f08a2ed..9d0337e 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -58,6 +58,7 @@
>  #include <asm/mmu_context.h>
>  #include <asm/processor.h>
>  #include <asm/stacktrace.h>
> +#include <asm/kexec.h>
>  
>  #ifdef CONFIG_CC_STACKPROTECTOR
>  #include <linux/stackprotector.h>
> @@ -107,6 +108,7 @@ void arch_cpu_idle_dead(void)
>  void machine_shutdown(void)
>  {
>  	disable_nonboot_cpus();
> +	machine_kexec_mask_interrupts();
>  }
>  
>  /*
> -- 
> Qualcomm Datacenter Technologies as an affiliate of Qualcomm Technologies, Inc. Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
> 
> 
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