Re: [Xen-devel] [V4 PATCH 1/2] x86/panic: Replace smp_send_stop() with kdump friendly version in panic path

[河合英宏 / KAWAI，HIDEHIRO <hidehiro.kawai.ez@xxxxxxxxxxx>]

Hi Xunlei,

> From: Xunlei Pang [mailto:xpang@xxxxxxxxxx]
> Sent: Tuesday, September 20, 2016 4:40 PM
> On 2016/08/15/ at 19:22, Hidehiro Kawai wrote:
> > Hi Dave,
> >
> > Thank you for the review.
> >
> >> From: Dave Young [mailto:dyoung@xxxxxxxxxx]
> >> Sent: Friday, August 12, 2016 12:17 PM
> >>
> >> 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.
> > So, I'll try another archives when I post patch set next time.
> 
> Hi Hidehiro Kawai,
> 
> What's the status of this patch set, are you going to send an updated version?

Sorry, I misunderstood what Dave said, and I thought I don't
need to revise the patch set.

Currently, this patch set is in -mm, then -next tree.
What I need to fix is only commit descriptions, so I'm going to
post revised descriptions as replies to this thread, and then
request to Andrew to replace them if there is no objection.
(or should I resend the whole patch set?)

Regards,
Hidehiro Kawai

> >>> 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.
> > As for Dom0 kernel, it doesn't use crash_kexec routines, and
> > it relies on panic notifier chain.  At the end of the chain,
> > xen_panic_event is called, and it issues a hypercall which
> > requests Hypervisor to execute kdump.  This means whether
> > crash_kexec_panic_notifiers is set or not, panic notifiers
> > are called after smp_send_stop.  Even if we save registers
> > in Dom0 kernel, they seem to be ignored (Hypervisor is responsible
> > for that).  This is why I kept the current behavior for Xen.
> >
> > For PV DomU kernel, kdump is not supported.  For PV HVM
> > DomU, I'm not sure what will happen on panic because I
> > couldn't boot PV HVM DomU and test it.  But I think it will
> > work similarly to baremetal kernels with extra cleanups
> > for Hypervisor.
> >
> > Best regards,
> >
> > Hidehiro Kawai
> >
> >>> 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@xxxxxxxxxx>
> >>> Fixes: f06e5153f4ae (kernel/panic.c: add "crash_kexec_post_notifiers" 
> >>> option)
> >>> Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@xxxxxxxxxxx>
> >>> Cc: Dave Young <dyoung@xxxxxxxxxx>
> >>> Cc: Baoquan He <bhe@xxxxxxxxxx>
> >>> Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
> >>> Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
> >>> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> >>> Cc: Daniel Walker <dwalker@xxxxxxxxxx>
> >>> Cc: Xunlei Pang <xpang@xxxxxxxxxx>
> >>> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> >>> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> >>> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> >>> Cc: Borislav Petkov <bp@xxxxxxx>
> >>> Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
> >>> Cc: Toshi Kani <toshi.kani@xxxxxxx>
> >>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> >>> ---
> >>>  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
> >>>
> >>>

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel