Subject: [PATCH v12 12/16] arm64: kdump: implement machine_crash_shutdown()

From: [email-masked] (AKASHI Takahiro)
Date: Thu, 10 Dec 2015 20:34:31 +0900

Marc,

I was back from my vacation.

On 11/27/2015 11:39 PM, Marc Zyngier wrote:
> On 24/11/15 22:25, Geoff Levand wrote:
>> From: AKASHI Takahiro <[email-masked]>
>>
>> kdump calls machine_crash_shutdown() to shut down non-boot cpus and
>> save registers' status in per-cpu ELF notes before starting the crash
>> dump kernel. See kernel_kexec().
>>
>> ipi_cpu_stop() is a bit modified and used to support this behavior.
>>
>> Signed-off-by: AKASHI Takahiro <[email-masked]>
>> ---
>>   arch/arm64/include/asm/kexec.h    | 34 +++++++++++++++++++++++++++++++++-
>>   arch/arm64/kernel/machine_kexec.c | 31 +++++++++++++++++++++++++++++--
>>   arch/arm64/kernel/smp.c           | 16 ++++++++++++++--
>>   3 files changed, 76 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
>> index 46d63cd..555a955 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, #16 *  0]\n"
>> +			"stp	 x2,   x3, [%3, #16 *  1]\n"
>> +			"stp	 x4,   x5, [%3, #16 *  2]\n"
>> +			"stp	 x6,   x7, [%3, #16 *  3]\n"
>> +			"stp	 x8,   x9, [%3, #16 *  4]\n"
>> +			"stp	x10,  x11, [%3, #16 *  5]\n"
>> +			"stp	x12,  x13, [%3, #16 *  6]\n"
>> +			"stp	x14,  x15, [%3, #16 *  7]\n"
>> +			"stp	x16,  x17, [%3, #16 *  8]\n"
>> +			"stp	x18,  x19, [%3, #16 *  9]\n"
>> +			"stp	x20,  x21, [%3, #16 * 10]\n"
>> +			"stp	x22,  x23, [%3, #16 * 11]\n"
>> +			"stp	x24,  x25, [%3, #16 * 12]\n"
>> +			"stp	x26,  x27, [%3, #16 * 13]\n"
>> +			"stp	x28,  x29, [%3, #16 * 14]\n"
>> +			"str	x30,	   [%3, #16 * 15]\n"
>> +			"mov	%0, sp\n"
>> +			"adr	%1, 1f\n"
>> +			"mrs	%2, spsr_el1\n"
>> +		"1:"
>> +			: "=r" (newregs->sp),
>> +			  "=r" (newregs->pc),
>> +			  "=r" (newregs->pstate)
>> +			: "r"  (&newregs->regs)
>> +			: "memory"
>> +		);
>
> I wonder how useful this thing is, given that it starts by corrupting
> whatever register is holding newregs->regs. Maybe this is not supposed
> to be accurate anyway...

I'm not quite sure about what part of my code you're mentioning here, but
crash_setup_regs() is solely called by crash_kexec(), and panic() is
the only caller of crash_kexec() with NULL argument which, in turn, is
used as 'oldregs' in crash_setup_regs().

Given this fact, I think that the values saved in newregs as indicated above
will be the best estimate of current cpu contexts.

The other caller of crash_kexec() is die() in traps.c, but here we call
it with explicit cpu contexts at exception.

>
>> +	}
>>   }
>>
>>   #endif /* !defined(__ASSEMBLY__) */
>> diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
>> index da28a26..d2d7e90 100644
>> --- a/arch/arm64/kernel/machine_kexec.c
>> +++ b/arch/arm64/kernel/machine_kexec.c
>> @@ -9,6 +9,7 @@
>>    * published by the Free Software Foundation.
>>    */
>>
>> +#include <linux/kernel.h>
>>   #include <linux/kexec.h>
>>   #include <linux/of_fdt.h>
>>   #include <linux/slab.h>
>> @@ -23,6 +24,7 @@
>>   extern const unsigned char arm64_relocate_new_kernel[];
>>   extern const unsigned long arm64_relocate_new_kernel_size;
>>
>> +bool in_crash_kexec;
>>   static unsigned long kimage_start;
>>
>>   /**
>> @@ -203,13 +205,38 @@ void machine_kexec(struct kimage *kimage)
>>   	 */
>>
>>   	cpu_soft_restart(virt_to_phys(cpu_reset),
>> -		is_hyp_mode_available(),
>> +		in_crash_kexec ? 0 : is_hyp_mode_available(),
>>   		reboot_code_buffer_phys, kimage->head, kimage_start);
>>
>>   	BUG(); /* Should never get here. */
>>   }
>>
>> +/**
>> + * machine_crash_shutdown - shutdown non-boot cpus and save registers
>> + */
>>   void machine_crash_shutdown(struct pt_regs *regs)
>>   {
>> -	/* Empty routine needed to avoid build errors. */
>> +	struct pt_regs dummy_regs;
>> +	int cpu;
>> +
>> +	local_irq_disable();
>> +
>> +	in_crash_kexec = true;
>> +
>> +	/*
>> +	 * clear and initialize the per-cpu info. This is necessary
>> +	 * because, otherwise, slots for offline cpus would never be
>> +	 * filled up. See smp_send_stop().
>> +	 */
>> +	memset(&dummy_regs, 0, sizeof(dummy_regs));
>> +	for_each_possible_cpu(cpu)
>> +		crash_save_cpu(&dummy_regs, cpu);
>> +
>> +	/* shutdown non-boot cpus */
>> +	smp_send_stop();
>> +
>> +	/* for boot cpu */
>> +	crash_save_cpu(regs, smp_processor_id());
>> +
>> +	pr_info("Starting crashdump kernel...\n");
>>   }
>> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
>> index b1adc51..15aabef 100644
>> --- a/arch/arm64/kernel/smp.c
>> +++ b/arch/arm64/kernel/smp.c
>> @@ -37,6 +37,7 @@
>>   #include <linux/completion.h>
>>   #include <linux/of.h>
>>   #include <linux/irq_work.h>
>> +#include <linux/kexec.h>
>>
>>   #include <asm/alternative.h>
>>   #include <asm/atomic.h>
>> @@ -54,6 +55,8 @@
>>   #include <asm/ptrace.h>
>>   #include <asm/virt.h>
>>
>> +#include "cpu-reset.h"
>> +
>>   #define CREATE_TRACE_POINTS
>>   #include <trace/events/ipi.h>
>>
>> @@ -683,8 +686,12 @@ 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)
>>   {
>> +#ifdef CONFIG_KEXEC
>> +	/* printing messages may slow down the shutdown. */
>> +	if (!in_crash_kexec)
>> +#endif
>>   	if (system_state == SYSTEM_BOOTING ||
>>   	    system_state == SYSTEM_RUNNING) {
>>   		raw_spin_lock(&stop_lock);
>
> Irrespective of how useful this change is, how about having a predicate
> instead? Something like:
>
> static inline bool is_in_crash_kexec(void)
> {
> #ifdef CONFIG_KEXEC
> 	return in_crash_kexec;
> #else
> 	return false;
> #endif
> }

OK, I will take your idea.

> located in machine_kexec.c (making the in_crash_kernel static), and then

but cannot make in_crash_kernel static because it is also used in both smp.c
and machine_kexec.c.

> 	if (!is_in_crash_kexec() && (systen_state == ... || ...) {
>
> It would certainly look better.

Thanks,
-Takahiro AKASHI

>> @@ -697,6 +704,11 @@ static void ipi_cpu_stop(unsigned int cpu)
>>
>>   	local_irq_disable();
>>
>> +#ifdef CONFIG_KEXEC
>> +	if (in_crash_kexec)
>> +		crash_save_cpu(regs, cpu);
>> +#endif /* CONFIG_KEXEC */
>> +
>
> Same here.
>
>>   	while (1)
>>   		cpu_relax();
>>   }
>> @@ -727,7 +739,7 @@ void handle_IPI(int ipinr, struct pt_regs *regs)
>>
>>   	case IPI_CPU_STOP:
>>   		irq_enter();
>> -		ipi_cpu_stop(cpu);
>> +		ipi_cpu_stop(cpu, regs);
>>   		irq_exit();
>>   		break;
>>
>>
>
> Thanks,
>
> 	M.
>