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 <takahiro.akashi at linaro.org>
>>
>> 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 <takahiro.akashi at linaro.org>
>> ---
>> 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.
>
