linux-kernel - Re: [v2 2/5] arm64: kdump: implement machine_crash

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Date:	Fri, 24 Apr 2015 11:39:00 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	AKASHI Takahiro <takahiro.akashi@...aro.org>
Cc:	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	"vgoyal@...hat.com" <vgoyal@...hat.com>,
	"hbabus@...ibm.com" <hbabus@...ibm.com>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"geoff@...radead.org" <geoff@...radead.org>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"broonie@...nel.org" <broonie@...nel.org>,
	"david.griego@...aro.org" <david.griego@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, marc.zyngier@....com
Subject: Re: [v2 2/5] arm64: kdump: implement machine_crash_shutdown()

On Fri, Apr 24, 2015 at 08:53:05AM +0100, AKASHI Takahiro wrote:
> kdump calls machine_crash_shutdown() to shut down non-boot cpus and
> save per-cpu general-purpose registers before restarting the crash dump
> kernel. See kernel_kexec().
> ipi_cpu_stop() is used and a bit modified to support this behavior.
> 
> Signed-off-by: AKASHI Takahiro <takahiro.akashi@...aro.org>
> ---
>  arch/arm64/include/asm/kexec.h    |   34 ++++++++++++++++++++++-
>  arch/arm64/kernel/machine_kexec.c |   55 ++++++++++++++++++++++++++++++++++++-
>  arch/arm64/kernel/smp.c           |   12 ++++++--
>  3 files changed, 97 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
> index 3530ff5..eaf3fcb 100644
> --- a/arch/arm64/include/asm/kexec.h
> +++ b/arch/arm64/include/asm/kexec.h
> @@ -30,6 +30,8 @@
>  
>  #if !defined(__ASSEMBLY__)
>  
> +extern bool in_crash_kexec;
> +
>  /**
>   * crash_setup_regs() - save registers for the panic kernel
>   *
> @@ -40,7 +42,37 @@
>  static inline void crash_setup_regs(struct pt_regs *newregs,
>  				    struct pt_regs *oldregs)
>  {
> -	/* Empty routine needed to avoid build errors. */
> +	if (oldregs) {
> +		memcpy(newregs, oldregs, sizeof(*newregs));
> +	} else {
> +		__asm__ __volatile__ (
> +			"stp	 x0,   x1, [%3]\n\t"

Why the tabs?

Please use #16 * N as the offset for consistency with entry.S, with 0
for the first N.

[...]

> +static void machine_kexec_mask_interrupts(void)
> +{
> +	unsigned int i;
> +	struct irq_desc *desc;
> +
> +	for_each_irq_desc(i, desc) {
> +		struct irq_chip *chip;
> +
> +		chip = irq_desc_get_chip(desc);
> +		if (!chip)
> +			continue;
> +
> +		if (chip->irq_eoi && irqd_irq_inprogress(&desc->irq_data))
> +			chip->irq_eoi(&desc->irq_data);
> +
> +		if (chip->irq_mask)
> +			chip->irq_mask(&desc->irq_data);
> +
> +		if (chip->irq_disable && !irqd_irq_disabled(&desc->irq_data))
> +			chip->irq_disable(&desc->irq_data);
> +	}
> +}

I'm surprised that this isn't left to the irqchip driver init code in
the crash kernel. For all we know this state could be corrupt anyway.

Is there any reason we can't get the GIC driver to nuke all of this at
probe time?

[...]

> @@ -542,7 +543,7 @@ static DEFINE_RAW_SPINLOCK(stop_lock);
>  /*
>   * ipi_cpu_stop - handle IPI from smp_send_stop()
>   */
> -static void ipi_cpu_stop(unsigned int cpu)
> +static void ipi_cpu_stop(unsigned int cpu, struct pt_regs *regs)
>  {
>  	if (system_state == SYSTEM_BOOTING ||
>  	    system_state == SYSTEM_RUNNING) {
> @@ -556,6 +557,13 @@ static void ipi_cpu_stop(unsigned int cpu)
>  
>  	local_irq_disable();
>  
> +#ifdef CONFIG_KEXEC
> +	if (in_crash_kexec) {
> +		crash_save_cpu(regs, cpu);
> +		flush_cache_all();

Any cache maintenance will need to be by VA; flush_cache_all doesn't do
what the name implies, though may appear to work by chance.

Is kdump implemented for ARM? I don't see equivalent for in the arch/arm
ipi_cpu_stop.

Mark.
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