On 10/12/15 11:34, AKASHI Takahiro wrote:
> 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().
You have this assembly sequence:
stp x0, x1, [%3, #16 * 0]
[...]
where %3 itself is one of the x[0..30] registers. So you are saving
things that have already been corrupted by the saving procedure. Not
sure how useful that is, but as I said, maybe it is not supposed to be
completely accurate.
> 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.
smp.c only reads from in_crash_kernel (at least from what I can see in
this patch), so it should be able to use the accessor.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
