Re: [Qemu-devel] [PATCH] APIC: add NMI and SMI IPI support

[Jan Kiszka <jan.kiszka@siemens.com>]

Robi Yagel wrote:
> Hello,
> Thanks for the patch,

Nice to hear that there is interest in this. :)

> if you can, please advice on the proper place to add
> periodic generation of SMI/NMIs in order to simulate, e.g., a watchdog (and the
> needed parameters - except for CPU_INTERRUPT_NMI...)

Yeah, I also thought about NMI watchdog emulation while adding
CPU_INTERRUPT_NMI, but it took a bit more effort to understand what
pieces are missing. It should be a fairly useful feature for testing NMI
interaction with new kernel code and maybe even catching nasty races
that way (whenever you happen to work on such things, like I do ;) ).
Also, we need NMI delivery for custom hardware emulation here. So there
might be broader use for CPU_INTERRUPT_NMI in the future.

However, find some experimental watchdog-enabler patch below. It allows
to use nmi_watchdog=1 (i.e. the IO-APIC variant) with Linux, without any
visible regression of normal IRQ delivery (but I only lightly tested it
on top of the kvm-userspace qemu, that's why "experimental").

A performance counter based NMI watchdog is surely doable as well, but
it takes a bit more effort. You would have to decide first what
perf-counter features should be emulated and how cleanly, even if you
only want to (mis-)use it for watchdog services. I'm lacking time for
this right now.

Jan

-- 
Siemens AG, Corporate Technology, CT SE 2
Corporate Competence Center Embedded Linux


---
 hw/apic.c |   38 +++++++++++++++++++++++++++++++++-----
 hw/pc.c   |    2 +-
 hw/pc.h   |    3 +++
 3 files changed, 37 insertions(+), 6 deletions(-)

Index: b/hw/apic.c
===================================================================
--- a/hw/apic.c
+++ b/hw/apic.c
@@ -166,6 +166,37 @@ static inline void reset_bit(uint32_t *t
     tab[i] &= ~mask;
 }
 
+void apic_local_deliver(CPUState *env, int vector)
+{
+    APICState *s = env->apic_state;
+    uint32_t lvt = s->lvt[vector];
+    int trigger_mode;
+
+    if (lvt & APIC_LVT_MASKED)
+        return;
+
+    switch ((lvt >> 8) & 7) {
+    case APIC_DM_SMI:
+        cpu_interrupt(env, CPU_INTERRUPT_SMI);
+        break;
+
+    case APIC_DM_NMI:
+        cpu_interrupt(env, CPU_INTERRUPT_NMI);
+        break;
+
+    case APIC_DM_EXTINT:
+        cpu_interrupt(env, CPU_INTERRUPT_HARD);
+        break;
+
+    case APIC_DM_FIXED:
+        trigger_mode = APIC_TRIGGER_EDGE;
+        if ((vector == APIC_LVT_LINT0 || vector == APIC_LVT_LINT1) &&
+            (lvt & APIC_LVT_LEVEL_TRIGGER))
+            trigger_mode = APIC_TRIGGER_LEVEL;
+        apic_set_irq(s, lvt & 0xff, trigger_mode);
+    }
+}
+
 #define foreach_apic(apic, deliver_bitmask, code) \
 {\
     int __i, __j, __mask;\
@@ -504,8 +535,7 @@ int apic_accept_pic_intr(CPUState *env)
 
     if (s->id == 0 &&
         ((s->apicbase & MSR_IA32_APICBASE_ENABLE) == 0 ||
-         ((lvt0 & APIC_LVT_MASKED) == 0 &&
-          ((lvt0 >> 8) & 0x7) == APIC_DM_EXTINT)))
+         (lvt0 & APIC_LVT_MASKED) == 0))
         return 1;
 
     return 0;
@@ -556,9 +586,7 @@ static void apic_timer(void *opaque)
 {
     APICState *s = opaque;
 
-    if (!(s->lvt[APIC_LVT_TIMER] & APIC_LVT_MASKED)) {
-        apic_set_irq(s, s->lvt[APIC_LVT_TIMER] & 0xff, APIC_TRIGGER_EDGE);
-    }
+    apic_local_deliver(s->cpu_env, APIC_LVT_TIMER);
     apic_timer_update(s, s->next_time);
 }
 
Index: b/hw/pc.c
===================================================================
--- a/hw/pc.c
+++ b/hw/pc.c
@@ -115,7 +115,7 @@ static void pic_irq_request(void *opaque
 {
     CPUState *env = opaque;
     if (level && apic_accept_pic_intr(env))
-        cpu_interrupt(env, CPU_INTERRUPT_HARD);
+        apic_local_deliver(env, APIC_LINT0);
 }
 
 /* PC cmos mappings */
Index: b/hw/pc.h
===================================================================
--- a/hw/pc.h
+++ b/hw/pc.h
@@ -39,8 +39,11 @@ void irq_info(void);
 /* APIC */
 typedef struct IOAPICState IOAPICState;
 
+#define APIC_LINT0	3
+
 int apic_init(CPUState *env);
 int apic_accept_pic_intr(CPUState *env);
+void apic_local_deliver(CPUState *env, int vector);
 int apic_get_interrupt(CPUState *env);
 IOAPICState *ioapic_init(void);
 void ioapic_set_irq(void *opaque, int vector, int level);