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

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Message-ID: <55C43319.3070906@linaro.org>
Date:	Fri, 07 Aug 2015 13:24:57 +0900
From:	AKASHI Takahiro <takahiro.akashi@...aro.org>
To:	Marc Zyngier <marc.zyngier@....com>,
	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()

Marc,

On 08/07/2015 12:51 AM, Marc Zyngier wrote:
> 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.

Please don't purge the page from your cache for a while :)

>> 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).

Thank you.
Please note that the same function, machine_kexec_mask_interrupts(),
is already there on arm(/kernel/machine_kexec.c).

Well, kexec/kdump stuff is not dead.
Hopefully I and Geoff will submit a full series of patchset in a few weeks
although the main logic will be the same.

>>
>> 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).

Aha, I should remember that arm has "multiple personalities."

-Takahiro AKASHI

> Thanks,
>
> 	M.
>
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