Re: [v2 2/5] arm64: kdump: implement machine_crash_shutdown()

[AKASHI Takahiro]

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@xxxxxxxxxx>
> > > > > ---
> > > > >    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.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/