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Date: Fri, 12 Aug 2016 11:16:33 +0800
From: Dave Young <dyoung@...hat.com>
To: Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Baoquan He <bhe@...hat.com>,
Ralf Baechle <ralf@...ux-mips.org>, linux-mips@...ux-mips.org,
xen-devel@...ts.xenproject.org, Toshi Kani <toshi.kani@....com>,
Xunlei Pang <xpang@...hat.com>, x86@...nel.org,
kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
HATAYAMA Daisuke <d.hatayama@...fujitsu.com>,
Ingo Molnar <mingo@...hat.com>,
David Vrabel <david.vrabel@...rix.com>,
"H. Peter Anvin" <hpa@...or.com>,
Daniel Walker <dwalker@...o99.com>,
Thomas Gleixner <tglx@...utronix.de>,
Borislav Petkov <bp@...e.de>, Vivek Goyal <vgoyal@...hat.com>,
Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [V4 PATCH 1/2] x86/panic: Replace smp_send_stop() with kdump
friendly version in panic path
Hi Hidehiro
Thanks for the update.
On 08/10/16 at 05:09pm, Hidehiro Kawai wrote:
> Daniel Walker reported problems which happens when
> crash_kexec_post_notifiers kernel option is enabled
> (https://lkml.org/lkml/2015/6/24/44).
>
> In that case, smp_send_stop() is called before entering kdump routines
> which assume other CPUs are still online. As the result, for x86,
> kdump routines fail to save other CPUs' registers and disable
> virtualization extensions.
Seems you simplified the changelog, but I think a little more details
will be helpful to understand the patch. You know sometimes lkml.org
does not work well.
>
> To fix this problem, call a new kdump friendly function,
> crash_smp_send_stop(), instead of the smp_send_stop() when
> crash_kexec_post_notifiers is enabled. crash_smp_send_stop() is a
> weak function, and it just call smp_send_stop(). Architecture
> codes should override it so that kdump can work appropriately.
> This patch only provides x86-specific version.
>
> For Xen's PV kernel, just keep the current behavior.
Could you explain a bit about above Xen PV kernel behavior?
BTW, this version looks better, I think I'm fine with this version
besides of the questions about changelog.
>
> Changes in V4:
> - Keep to use smp_send_stop if crash_kexec_post_notifiers is not set
> - Rename panic_smp_send_stop to crash_smp_send_stop
> - Don't change the behavior for Xen's PV kernel
>
> Changes in V3:
> - Revise comments, description, and symbol names
>
> Changes in V2:
> - Replace smp_send_stop() call with crash_kexec version which
> saves cpu states and cleans up VMX/SVM
> - Drop a fix for Problem 1 at this moment
>
> Reported-by: Daniel Walker <dwalker@...o99.com>
> Fixes: f06e5153f4ae (kernel/panic.c: add "crash_kexec_post_notifiers" option)
> Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>
> Cc: Dave Young <dyoung@...hat.com>
> Cc: Baoquan He <bhe@...hat.com>
> Cc: Vivek Goyal <vgoyal@...hat.com>
> Cc: Eric Biederman <ebiederm@...ssion.com>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: Daniel Walker <dwalker@...o99.com>
> Cc: Xunlei Pang <xpang@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: David Vrabel <david.vrabel@...rix.com>
> Cc: Toshi Kani <toshi.kani@....com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> ---
> arch/x86/include/asm/kexec.h | 1 +
> arch/x86/include/asm/smp.h | 1 +
> arch/x86/kernel/crash.c | 22 +++++++++++++++++---
> arch/x86/kernel/smp.c | 5 ++++
> kernel/panic.c | 47 ++++++++++++++++++++++++++++++++++++------
> 5 files changed, 66 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
> index d2434c1..282630e 100644
> --- a/arch/x86/include/asm/kexec.h
> +++ b/arch/x86/include/asm/kexec.h
> @@ -210,6 +210,7 @@ struct kexec_entry64_regs {
>
> typedef void crash_vmclear_fn(void);
> extern crash_vmclear_fn __rcu *crash_vmclear_loaded_vmcss;
> +extern void kdump_nmi_shootdown_cpus(void);
>
> #endif /* __ASSEMBLY__ */
>
> diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
> index ebd0c16..f70989c 100644
> --- a/arch/x86/include/asm/smp.h
> +++ b/arch/x86/include/asm/smp.h
> @@ -50,6 +50,7 @@ struct smp_ops {
> void (*smp_cpus_done)(unsigned max_cpus);
>
> void (*stop_other_cpus)(int wait);
> + void (*crash_stop_other_cpus)(void);
> void (*smp_send_reschedule)(int cpu);
>
> int (*cpu_up)(unsigned cpu, struct task_struct *tidle);
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index 9616cf7..650830e 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -133,15 +133,31 @@ static void kdump_nmi_callback(int cpu, struct pt_regs *regs)
> disable_local_APIC();
> }
>
> -static void kdump_nmi_shootdown_cpus(void)
> +void kdump_nmi_shootdown_cpus(void)
> {
> nmi_shootdown_cpus(kdump_nmi_callback);
>
> disable_local_APIC();
> }
>
> +/* Override the weak function in kernel/panic.c */
> +void crash_smp_send_stop(void)
> +{
> + static int cpus_stopped;
> +
> + if (cpus_stopped)
> + return;
> +
> + if (smp_ops.crash_stop_other_cpus)
> + smp_ops.crash_stop_other_cpus();
> + else
> + smp_send_stop();
> +
> + cpus_stopped = 1;
> +}
> +
> #else
> -static void kdump_nmi_shootdown_cpus(void)
> +void crash_smp_send_stop(void)
> {
> /* There are no cpus to shootdown */
> }
> @@ -160,7 +176,7 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
> /* The kernel is broken so disable interrupts */
> local_irq_disable();
>
> - kdump_nmi_shootdown_cpus();
> + crash_smp_send_stop();
>
> /*
> * VMCLEAR VMCSs loaded on this cpu if needed.
> diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
> index 658777c..68f8cc2 100644
> --- a/arch/x86/kernel/smp.c
> +++ b/arch/x86/kernel/smp.c
> @@ -32,6 +32,8 @@
> #include <asm/nmi.h>
> #include <asm/mce.h>
> #include <asm/trace/irq_vectors.h>
> +#include <asm/kexec.h>
> +
> /*
> * Some notes on x86 processor bugs affecting SMP operation:
> *
> @@ -342,6 +344,9 @@ struct smp_ops smp_ops = {
> .smp_cpus_done = native_smp_cpus_done,
>
> .stop_other_cpus = native_stop_other_cpus,
> +#if defined(CONFIG_KEXEC_CORE)
> + .crash_stop_other_cpus = kdump_nmi_shootdown_cpus,
> +#endif
> .smp_send_reschedule = native_smp_send_reschedule,
>
> .cpu_up = native_cpu_up,
> diff --git a/kernel/panic.c b/kernel/panic.c
> index ca8cea1..e6480e2 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -71,6 +71,32 @@ void __weak nmi_panic_self_stop(struct pt_regs *regs)
> panic_smp_self_stop();
> }
>
> +/*
> + * Stop other CPUs in panic. Architecture dependent code may override this
> + * with more suitable version. For example, if the architecture supports
> + * crash dump, it should save registers of each stopped CPU and disable
> + * per-CPU features such as virtualization extensions.
> + */
> +void __weak crash_smp_send_stop(void)
> +{
> + static int cpus_stopped;
> +
> + /*
> + * This function can be called twice in panic path, but obviously
> + * we execute this only once.
> + */
> + if (cpus_stopped)
> + return;
> +
> + /*
> + * Note smp_send_stop is the usual smp shutdown function, which
> + * unfortunately means it may not be hardened to work in a panic
> + * situation.
> + */
> + smp_send_stop();
> + cpus_stopped = 1;
> +}
> +
> atomic_t panic_cpu = ATOMIC_INIT(PANIC_CPU_INVALID);
>
> /*
> @@ -164,14 +190,21 @@ void panic(const char *fmt, ...)
> if (!_crash_kexec_post_notifiers) {
> printk_nmi_flush_on_panic();
> __crash_kexec(NULL);
> - }
>
> - /*
> - * Note smp_send_stop is the usual smp shutdown function, which
> - * unfortunately means it may not be hardened to work in a panic
> - * situation.
> - */
> - smp_send_stop();
> + /*
> + * Note smp_send_stop is the usual smp shutdown function, which
> + * unfortunately means it may not be hardened to work in a
> + * panic situation.
> + */
> + smp_send_stop();
> + } else {
> + /*
> + * If we want to do crash dump after notifier calls and
> + * kmsg_dump, we will need architecture dependent extra
> + * works in addition to stopping other CPUs.
> + */
> + crash_smp_send_stop();
> + }
>
> /*
> * Run any panic handlers, including those that might need to
>
>
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