RE: [Xen-devel] Re: One question to IST stack for PV guest

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Sat, 2009-12-19 at 14:41 +0000, Jiang, Yunhong wrote:
> Can SysRQ-L be used to check dead-locked CPU's state?

As I understand it yes, it can be used to debug CPUs hung with
interrupts disabled.

>  And if we have no NMI support, we may lost that part.

I think so. It's still useful for other classes of hang (i.e. those
where interrupts are enabled).

Ian.

> 
> --jyh
> 
> >-----Original Message-----
> >From: Ian Campbell [mailto:Ian.Campbell@xxxxxxxxxx]
> >Sent: Saturday, December 19, 2009 5:25 PM
> >To: Jeremy Fitzhardinge
> >Cc: Jiang, Yunhong; Kleen, Andi; xen-devel@xxxxxxxxxxxxxxxxxxx; Keir Fraser; 
> >Jan
> >Beulich
> >Subject: Re: [Xen-devel] Re: One question to IST stack for PV guest
> >
> >On Fri, 2009-12-18 at 21:21 +0000, Jeremy Fitzhardinge wrote:
> >>
> >> > BTW, Jeremy, seems vNMI support is not included in pvops dom0, will
> >> it be supported in future?
> >> >
> >>
> >> There's been no call for it so far, so I hadn't worried about it much.
> >> I was thinking it might be useful as a debug tool, but I don't know
> >> what it gets used for normally.
> >
> >SysRQ-L (show all cpus) uses it via arch_trigger_all_cpu_backtrace()
> >which is a bit of a problem even in a domU because it goes to
> >apic->send_IPI_all(NMI_VECTOR) which ends up "BUG: unable to handle
> >kernel paging request" in default_send_IPI_mask_logical.
> >
> >I started adding a new smp_op to handle allow this function to be
> >overidden yesterday (WIP appended) but having some sort of NMI support
> >would be useful so reduce the differences with native on the receiving
> >end, instead of using smp_call_function.
> >
> >Ian.
> >
> >
> >diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
> >index 1e79678..00ef5f7 100644
> >--- a/arch/x86/include/asm/smp.h
> >+++ b/arch/x86/include/asm/smp.h
> >@@ -60,6 +60,8 @@ struct smp_ops {
> >
> >     void (*send_call_func_ipi)(const struct cpumask *mask);
> >     void (*send_call_func_single_ipi)(int cpu);
> >+
> >+    void (*send_nmi_ipi)(void);
> > };
> >
> > /* Globals due to paravirt */
> >@@ -126,6 +128,11 @@ static inline void 
> >arch_send_call_function_ipi_mask(const
> >struct cpumask *mask)
> >     smp_ops.send_call_func_ipi(mask);
> > }
> >
> >+static inline void smp_send_nmi_ipi(void)
> >+{
> >+    smp_ops.send_nmi_ipi();
> >+}
> >+
> > void cpu_disable_common(void);
> > void native_smp_prepare_boot_cpu(void);
> > void native_smp_prepare_cpus(unsigned int max_cpus);
> >@@ -139,6 +146,8 @@ void play_dead_common(void);
> > void native_send_call_func_ipi(const struct cpumask *mask);
> > void native_send_call_func_single_ipi(int cpu);
> >
> >+void native_send_nmi_ipi(void);
> >+
> > void smp_store_cpu_info(int id);
> > #define cpu_physical_id(cpu)        per_cpu(x86_cpu_to_apicid, cpu)
> >
> >diff --git a/arch/x86/kernel/apic/nmi.c b/arch/x86/kernel/apic/nmi.c
> >index 7ff61d6..40c1414 100644
> >--- a/arch/x86/kernel/apic/nmi.c
> >+++ b/arch/x86/kernel/apic/nmi.c
> >@@ -561,7 +561,7 @@ void arch_trigger_all_cpu_backtrace(void)
> >     cpumask_copy(&backtrace_mask, cpu_online_mask);
> >
> >     printk(KERN_INFO "sending NMI to all CPUs:\n");
> >-    apic->send_IPI_all(NMI_VECTOR);
> >+    smp_send_nmi_ipi();
> >
> >     /* Wait for up to 10 seconds for all CPUs to do the backtrace */
> >     for (i = 0; i < 10 * 1000; i++) {
> >diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
> >index ec1de97..f53437f 100644
> >--- a/arch/x86/kernel/smp.c
> >+++ b/arch/x86/kernel/smp.c
> >@@ -146,6 +146,11 @@ void native_send_call_func_ipi(const struct cpumask
> >*mask)
> >     free_cpumask_var(allbutself);
> > }
> >
> >+void native_send_nmi_ipi(void)
> >+{
> >+    apic->send_IPI_all(NMI_VECTOR);
> >+}
> >+
> > /*
> >  * this function calls the 'stop' function on all other CPUs in the system.
> >  */
> >@@ -236,5 +241,7 @@ struct smp_ops smp_ops = {
> >
> >     .send_call_func_ipi     = native_send_call_func_ipi,
> >     .send_call_func_single_ipi = native_send_call_func_single_ipi,
> >+
> >+    .send_nmi_ipi           = native_send_nmi_ipi,
> > };
> > EXPORT_SYMBOL_GPL(smp_ops);
> >diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
> >index 360f8d8..986f372 100644
> >--- a/arch/x86/xen/smp.c
> >+++ b/arch/x86/xen/smp.c
> >@@ -20,6 +20,7 @@
> > #include <asm/desc.h>
> > #include <asm/pgtable.h>
> > #include <asm/cpu.h>
> >+#include <asm/nmi.h>
> >
> > #include <xen/interface/xen.h>
> > #include <xen/interface/vcpu.h>
> >@@ -456,6 +457,16 @@ static irqreturn_t 
> >xen_call_function_single_interrupt(int
> >irq, void *dev_id)
> >     return IRQ_HANDLED;
> > }
> >
> >+static void xen_nmi_ipi_func(void *info)
> >+{
> >+    nmi_watchdog_tick(task_pt_regs(current), 0/*reason*/);
> >+}
> >+
> >+static void xen_send_nmi_ipi(void)
> >+{
> >+    smp_call_function(xen_nmi_ipi_func, NULL, 0);
> >+}
> >+
> > static const struct smp_ops xen_smp_ops __initdata = {
> >     .smp_prepare_boot_cpu = xen_smp_prepare_boot_cpu,
> >     .smp_prepare_cpus = xen_smp_prepare_cpus,
> >@@ -471,6 +482,8 @@ static const struct smp_ops xen_smp_ops __initdata = {
> >
> >     .send_call_func_ipi = xen_smp_send_call_function_ipi,
> >     .send_call_func_single_ipi = xen_smp_send_call_function_single_ipi,
> >+
> >+    .send_nmi_ipi = xen_send_nmi_ipi,
> > };
> >
> > void __init xen_smp_init(void)
> >
> 



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