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Re: [Xen-devel] [PATCH v2 3/6] x86: track when in #MC context



Hi Roger,

On 18/02/2020 09:48, Roger Pau Monné wrote:
On Mon, Feb 17, 2020 at 07:29:29PM +0000, Julien Grall wrote:
Hi Roger,

On 17/02/2020 18:43, Roger Pau Monne wrote:
Add helpers to track when executing in #MC context. This is modeled
after the in_irq helpers.

Note that there are no users of in_mc() introduced by the change,
further users will be added by followup changes.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
   xen/arch/x86/cpu/mcheck/mce.c | 2 ++
   xen/include/asm-x86/hardirq.h | 5 +++++
   xen/include/xen/irq_cpustat.h | 1 +
   3 files changed, 8 insertions(+)

diff --git a/xen/arch/x86/cpu/mcheck/mce.c b/xen/arch/x86/cpu/mcheck/mce.c
index d61e582af3..93ed5752ac 100644
--- a/xen/arch/x86/cpu/mcheck/mce.c
+++ b/xen/arch/x86/cpu/mcheck/mce.c
@@ -93,7 +93,9 @@ void x86_mce_vector_register(x86_mce_vector_t hdlr)
   void do_machine_check(const struct cpu_user_regs *regs)
   {
+    mc_enter();
       _machine_check_vector(regs);
+    mc_exit();
   }
   /*
diff --git a/xen/include/asm-x86/hardirq.h b/xen/include/asm-x86/hardirq.h
index 34e1b49260..af3eab6a4d 100644
--- a/xen/include/asm-x86/hardirq.h
+++ b/xen/include/asm-x86/hardirq.h
@@ -8,6 +8,7 @@ typedef struct {
        unsigned int __softirq_pending;
        unsigned int __local_irq_count;
        unsigned int __nmi_count;
+       unsigned int mc_count;
        bool_t __mwait_wakeup;
   } __cacheline_aligned irq_cpustat_t;
@@ -18,6 +19,10 @@ typedef struct {
   #define irq_enter()  (local_irq_count(smp_processor_id())++)
   #define irq_exit()   (local_irq_count(smp_processor_id())--)
+#define in_mc()        (mc_count(smp_processor_id()) != 0)
+#define mc_enter()     (mc_count(smp_processor_id())++)
+#define mc_exit()      (mc_count(smp_processor_id())--)
+
   void ack_bad_irq(unsigned int irq);
   extern void apic_intr_init(void);
diff --git a/xen/include/xen/irq_cpustat.h b/xen/include/xen/irq_cpustat.h
index 73629f6ec8..12b932fc39 100644
--- a/xen/include/xen/irq_cpustat.h
+++ b/xen/include/xen/irq_cpustat.h
@@ -26,5 +26,6 @@ extern irq_cpustat_t irq_stat[];
   #define local_irq_count(cpu) __IRQ_STAT((cpu), __local_irq_count)
   #define nmi_count(cpu)               __IRQ_STAT((cpu), __nmi_count)
   #define mwait_wakeup(cpu)    __IRQ_STAT((cpu), __mwait_wakeup)
+#define mc_count(cpu)          __IRQ_STAT((cpu), mc_count)

The header is only meant to contain arch-independent IRQ stats (see comment
a few lines above). This is unlikely to be used on Arm, so can you move this
into an x86 specific header?

Now that I look at it, there's also nmi_count and mwait_wakeup defined
in irq_cpustat.h which won't build if used on Arm, since the fields
don't exist in the Arm version of irq_cpustat_t.

I would prefer if we don't introduce more cases in xen/irq_cpustat.h. It would be good to remove nmi_count() and mwait_wakeup() from the common header, but that's a separate cleanup.

Cheers,

--
Julien Grall

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