Re: [Xen-devel] [PATCH v2] x86: show remote CPU state upon fatal NMI or unknown MCE

2016-06-16 Thread Andrew Cooper
On 16/06/16 12:26, Jan Beulich wrote:
> @@ -570,6 +589,15 @@ void fatal_trap(const struct cpu_user_re
>  printk("Faulting linear address: %p\n", _p(cr2));
>  show_page_walk(cr2);
>  }
> +if ( show_remote )
> +{
> +cpumask_andnot(_state_mask, _online_map,
> +   cpumask_of(smp_processor_id()));
> +set_nmi_callback(nmi_show_execution_state);
> +smp_send_nmi_allbutself();
> +while ( !cpumask_empty(_state_mask) )
> +cpu_relax();

Sorry about not noticing this before.  We need a maximum timeout here,
just like the nmi shootdown, in case one of the other cpus is already
stuck in an NMI handler, so we block the reboot/kexec.

With that fixed, Reviewed-by: Andrew Cooper 

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[Xen-devel] [PATCH v2] x86: show remote CPU state upon fatal NMI or unknown MCE

2016-06-16 Thread Jan Beulich
Quite frequently the watchdog would hit an innocent CPU, e.g. one
trying to acquire a spin lock a remote CPU holds for extended periods
of time, or a random CPU in TSC calbration rendezvous. In such cases
the register and stack dump for that CPU doesn't really help in the
analysis of the problem.

To keep things reasonable on large systems, only log CS:RIP by default.
This can be overridden via a new command line option such that full
register/stack state would get logged.

Signed-off-by: Jan Beulich 
---
v2: Pass flag to fatal_trap().

--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -198,6 +198,14 @@ Permit Xen to use Address Space Identifi
 tags the TLB entries with an ID per vcpu.  This allows for guest TLB flushes
 to be performed without the overhead of a complete TLB flush.
 
+### async-show-all
+> `= `
+
+> Default: `false`
+
+Forces all CPUs' full state to be logged upon certain fatal asynchronous
+exceptions (watchdog NMIs and unexpected MCEs).
+
 ### ats
 > `= `
 
--- a/xen/arch/x86/cpu/mcheck/mce.c
+++ b/xen/arch/x86/cpu/mcheck/mce.c
@@ -77,7 +77,7 @@ static void unexpected_machine_check(con
 {
 console_force_unlock();
 printk("Unexpected Machine Check Exception\n");
-fatal_trap(regs);
+fatal_trap(regs, 1);
 }
 
 
--- a/xen/arch/x86/nmi.c
+++ b/xen/arch/x86/nmi.c
@@ -488,7 +488,7 @@ bool_t nmi_watchdog_tick(const struct cp
 console_force_unlock();
 printk("Watchdog timer detects that CPU%d is stuck!\n",
smp_processor_id());
-fatal_trap(regs);
+fatal_trap(regs, 1);
 }
 } 
 else 
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -525,6 +525,25 @@ void vcpu_show_execution_state(struct vc
 vcpu_unpause(v);
 }
 
+static cpumask_t show_state_mask;
+static bool_t opt_show_all;
+boolean_param("async-show-all", opt_show_all);
+
+static int nmi_show_execution_state(const struct cpu_user_regs *regs, int cpu)
+{
+if ( !cpumask_test_cpu(cpu, _state_mask) )
+return 0;
+
+if ( opt_show_all )
+show_execution_state(regs);
+else
+printk(XENLOG_ERR "CPU%d @ %04x:%08lx (%pS)\n", cpu, regs->cs, 
regs->rip,
+   guest_mode(regs) ? _p(regs->rip) : NULL);
+cpumask_clear_cpu(cpu, _state_mask);
+
+return 1;
+}
+
 static const char *trapstr(unsigned int trapnr)
 {
 static const char * const strings[] = {
@@ -544,7 +563,7 @@ static const char *trapstr(unsigned int
  * are disabled). In such situations we can't do much that is safe. We try to
  * print out some tracing and then we just spin.
  */
-void fatal_trap(const struct cpu_user_regs *regs)
+void fatal_trap(const struct cpu_user_regs *regs, bool_t show_remote)
 {
 static DEFINE_PER_CPU(char, depth);
 unsigned int trapnr = regs->entry_vector;
@@ -570,6 +589,15 @@ void fatal_trap(const struct cpu_user_re
 printk("Faulting linear address: %p\n", _p(cr2));
 show_page_walk(cr2);
 }
+if ( show_remote )
+{
+cpumask_andnot(_state_mask, _online_map,
+   cpumask_of(smp_processor_id()));
+set_nmi_callback(nmi_show_execution_state);
+smp_send_nmi_allbutself();
+while ( !cpumask_empty(_state_mask) )
+cpu_relax();
+}
 }
 
 panic("FATAL TRAP: vector = %d (%s)\n"
@@ -1711,7 +1739,7 @@ void do_page_fault(struct cpu_user_regs
 {
 console_start_sync();
 printk("Xen SM%cP violation\n", (pf_type == smep_fault) ? 'E' : 
'A');
-fatal_trap(regs);
+fatal_trap(regs, 0);
 }
 
 if ( pf_type != real_fault )
@@ -1782,7 +1810,7 @@ void __init do_early_page_fault(struct c
 console_start_sync();
 printk("Early fatal page fault at %04x:%p (cr2=%p, ec=%04x)\n",
regs->cs, _p(regs->eip), _p(cr2), regs->error_code);
-fatal_trap(regs);
+fatal_trap(regs, 0);
 }
 }
 
@@ -3598,7 +3626,7 @@ static void pci_serr_error(const struct
 default:  /* 'fatal' */
 console_force_unlock();
 printk("\n\nNMI - PCI system error (SERR)\n");
-fatal_trap(regs);
+fatal_trap(regs, 0);
 }
 }
 
@@ -3613,7 +3641,7 @@ static void io_check_error(const struct
 default:  /* 'fatal' */
 console_force_unlock();
 printk("\n\nNMI - I/O ERROR\n");
-fatal_trap(regs);
+fatal_trap(regs, 0);
 }
 
 outb((inb(0x61) & 0x0f) | 0x08, 0x61); /* clear-and-disable IOCK */
@@ -3633,7 +3661,7 @@ static void unknown_nmi_error(const stru
 console_force_unlock();
 printk("Uhhuh. NMI received for unknown reason %02x.\n", reason);
 printk("Do you have a strange power saving mode enabled?\n");
-fatal_trap(regs);
+fatal_trap(regs, 0);
 }
 }
 
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -558,6 +558,7 @@