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

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Message-ID: <55C38269.8090907@arm.com>
Date:	Thu, 06 Aug 2015 16:51:05 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	AKASHI Takahiro <takahiro.akashi@...aro.org>,
	Mark Rutland <Mark.Rutland@....com>
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>
Subject: Re: [v2 2/5] arm64: kdump: implement machine_crash_shutdown()

Hi,

On 06/08/15 08:09, AKASHI Takahiro wrote:
> Marc, Mark
> 
> Sorry for not revisiting your comment below for a while.

Wow. It took me a few minutes to page the context back in.

> On 04/24/2015 07:43 PM, Marc Zyngier wrote:
>> On 24/04/15 11:39, Mark Rutland wrote:
>>> 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.
>>
>> Indeed, parsing the irqdesc list is a recipe for disaster. Who knows
>> which locks have been taken or simply corrupted, pointers nuked...
>>
>>> Is there any reason we can't get the GIC driver to nuke all of this at
>>> probe time?
> 
> Is it just enough to remove kexec_mask_interrupts() and add gic_eoi_irq()
> at the beginning of gic_cpu_init() in irq-gic.c and irq-gic-v3.c?

No, doing an EOI is definitely the wrong thing to do. If you do it in
the wrong order, you just screw up the GIC state machine. Plus, you have
no idea what to write there...

The only real solution is to zero the "active" registers.

>> This feels like the better option. I can cook a patch or two for that.
> 
> If you do, that will be much better :)

OK, I'll prepare something that we can merge at the same time kexec
comes back from the dead (if it ever does - I'm not holding my breath).

> 
> BTW, in arm-gic-v3.h, GICD_CTRL_ARE_NS is defined as
>      (1U << 4)
> but should it be 5?
> (I'm referring to the page 8-415 in IHI0069A.)

No, look at the definition ARE_NS has when the access is non-secure or
on a system supporting a single security state. The definition you're
referring to is for a secure access (firmware).

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...
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