[RFC,14/17] powerpc/book3e-64/kexec: Enable SMP release
mpe at ellerman.id.au
Tue Aug 18 14:51:41 AEST 2015
On Sat, 2015-18-07 at 20:08:51 UTC, Scott Wood wrote:
> booted_from_exec is similar to __run_at_load, except that it is set for
Also do you mind using __booted_from_kexec to keep the naming similar to the
other variables down there, and also make it clear it's low level guts.
I see you asked for them to be removed on the original patch but all the other
vars in there are named that way.
> regular kexec as well as kdump.
> The flag is needed because the SMP release mechanism for FSL book3e is
> different from when booting with normal hardware. In theory we could
> simulate the normal spin table mechanism, but not at the addresses
> U-Boot put in the device tree -- so there'd need to be even more
> communication between the kernel and kexec to set that up. Since
> there's already a similar flag being set (for kdump only), this seemed
> like a reasonable approach.
Yeah I guess it is. Obviously it'd be nicer if we didn't have to do it though.
> Unlike __run_at_kexec in http://patchwork.ozlabs.org/patch/257657/
> ("book3e/kexec/kdump: introduce a kexec kernel flag"), this flag is at
> a fixed address for ABI stability, and actually gets set properly in
> the kdump case (i.e. on the crash kernel, not on the crashing kernel).
> Signed-off-by: Scott Wood <scottwood at freescale.com>
> This depends on the kexec-tools patch "ppc64: Add a flag to tell the
> kernel it's booting from kexec":
> arch/powerpc/include/asm/smp.h | 1 +
> arch/powerpc/kernel/head_64.S | 15 +++++++++++++++
> arch/powerpc/kernel/setup_64.c | 14 +++++++++++++-
> arch/powerpc/platforms/85xx/smp.c | 16 ++++++++++++----
> 4 files changed, 41 insertions(+), 5 deletions(-)
> diff --git a/arch/powerpc/include/asm/smp.h b/arch/powerpc/include/asm/smp.h
> index 825663c..f9245df 100644
> --- a/arch/powerpc/include/asm/smp.h
> +++ b/arch/powerpc/include/asm/smp.h
> @@ -197,6 +197,7 @@ extern void generic_secondary_thread_init(void);
> extern unsigned long __secondary_hold_spinloop;
> extern unsigned long __secondary_hold_acknowledge;
> extern char __secondary_hold;
> +extern u32 booted_from_kexec;
> extern void __early_start(void);
> #endif /* __ASSEMBLY__ */
> diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
> index 1b77956..ae2d6b5 100644
> --- a/arch/powerpc/kernel/head_64.S
> +++ b/arch/powerpc/kernel/head_64.S
> @@ -91,6 +91,21 @@ __secondary_hold_spinloop:
> .llong 0x0
> + /* Do not move this variable as kexec-tools knows about it. */
> + . = 0x58
> + .globl booted_from_kexec
> + /*
> + * "nkxc" -- not (necessarily) from kexec by default
> + *
> + * This flag is set to 1 by a loader if the kernel is being
> + * booted by kexec. Older kexec-tools don't know about this
> + * flag, so platforms other than fsl-book3e should treat a value
> + * of "nkxc" as inconclusive. fsl-book3e relies on this to
> + * know how to release secondary cpus.
> + */
> + .long 0x6e6b7863
Couldn't we say that "nkxc" (whatever that stands for) means "unknown", and
have kexec-tools write "yes" to indicate yes. I realise that's not 100% bullet
proof, but it seems like it would be good enough. And it would mean we could
use the flag on other platforms if we ever want to.
Also "nkxc" ? "bfkx" ?
> diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
> index 505ec2c..baeddcc 100644
> --- a/arch/powerpc/kernel/setup_64.c
> +++ b/arch/powerpc/kernel/setup_64.c
> @@ -340,11 +340,23 @@ void early_setup_secondary(void)
> #endif /* CONFIG_SMP */
> #if defined(CONFIG_SMP) || defined(CONFIG_KEXEC)
> +static bool use_spinloop(void)
> +#ifdef CONFIG_PPC_FSL_BOOK3E
> + return booted_from_kexec == 1;
> + return true;
Ugh, more ifdefs.
return IS_ENABLED(CONFIG_PPC_FSL_BOOK3E) && (booted_from_kexec == 1);
If that works, I haven't checked. It's slightly less ugly?
> void smp_release_cpus(void)
> unsigned long *ptr;
> int i;
> + if (!use_spinloop())
> + return;
> DBG(" -> smp_release_cpus()\n");
> /* All secondary cpus are spinning on a common spinloop, release them
> @@ -524,7 +536,7 @@ void __init setup_system(void)
> * Freescale Book3e parts spin in a loop provided by firmware,
> * so smp_release_cpus() does nothing for them
> -#if defined(CONFIG_SMP) && !defined(CONFIG_PPC_FSL_BOOK3E)
> +#if defined(CONFIG_SMP)
Can you make that just #ifdef CONFIG_SMP.
> /* Release secondary cpus out of their spinloops at 0x60 now that
> * we can map physical -> logical CPU ids
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