[Qemu-devel] [PATCH 3/3] x86: Rework local IRQ delivery for APICs

[Jan Kiszka]

[ Refreshed and resent version of
 http://permalink.gmane.org/gmane.comp.emulators.qemu/23456 ]

This patch reworks the delivery of IRQs directed to a local APIC,
handling all requests in a central function, apic_local_deliver(),
analogue to apic_bus_deliver().

Futhermore, the APIC_LVT_LINT0 mask initialization is fixed for SMP.
Finally, virtual routing of the legacy PIT to the APICs is adopted in so
far that pic_irq_request() delivers interrupts through the LINT0 lines
of all APICs in the system. This routing allows for emulating the
IO-APIC NMI watchdog mechanism, including on SMP, which Linux exploits
via its nmi_watchdog=1.

Signed-off-by: Jan Kiszka <address@hidden>

---
hw/apic.c |   63 ++++++++++++++++++++++++++++++++++++++++++--------------------
hw/pc.c   |   15 ++++++++++----
hw/pc.h   |    3 ++
3 files changed, 57 insertions(+), 24 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;\
@@ -502,10 +533,8 @@ int apic_accept_pic_intr(CPUState *env)

    lvt0 = s->lvt[APIC_LVT_LINT0];

-    if (s->id == 0 &&
-        ((s->apicbase & MSR_IA32_APICBASE_ENABLE) == 0 ||
-         ((lvt0 & APIC_LVT_MASKED) == 0 &&
-          ((lvt0 >> 8) & 0x7) == APIC_DM_EXTINT)))
+    if ((s->apicbase & MSR_IA32_APICBASE_ENABLE) == 0 ||
+        (lvt0 & APIC_LVT_MASKED) == 0)
        return 1;

    return 0;
@@ -556,9 +585,7 @@ 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);
}

@@ -821,12 +848,14 @@ static void apic_reset(void *opaque)
    APICState *s = opaque;
    apic_init_ipi(s);

-    /*
-     * LINT0 delivery mode is set to ExtInt at initialization time
-     * typically by BIOS, so PIC interrupt can be delivered to the
-     * processor when local APIC is enabled.
-     */
-    s->lvt[APIC_LVT_LINT0] = 0x700;
+    if (s->id == 0) {
+        /*
+         * LINT0 delivery mode on CPU #0 is set to ExtInt at initialization
+         * time typically by BIOS, so PIC interrupt can be delivered to the
+         * processor when local APIC is enabled.
+         */
+        s->lvt[APIC_LVT_LINT0] = 0x700;
+    }
}

static CPUReadMemoryFunc *apic_mem_read[3] = {
@@ -851,19 +880,13 @@ int apic_init(CPUState *env)
    if (!s)
        return -1;
    env->apic_state = s;
-    apic_init_ipi(s);
    s->id = last_apic_id++;
    env->cpuid_apic_id = s->id;
    s->cpu_env = env;
    s->apicbase = 0xfee00000 |
        (s->id ? 0 : MSR_IA32_APICBASE_BSP) | MSR_IA32_APICBASE_ENABLE;

-    /*
-     * LINT0 delivery mode is set to ExtInt at initialization time
-     * typically by BIOS, so PIC interrupt can be delivered to the
-     * processor when local APIC is enabled.
-     */
-    s->lvt[APIC_LVT_LINT0] = 0x700;
+    apic_reset(s);

    /* XXX: mapping more APICs at the same memory location */
    if (apic_io_memory == 0) {
Index: b/hw/pc.c
===================================================================
--- a/hw/pc.c
+++ b/hw/pc.c
@@ -113,9 +113,16 @@ int cpu_get_pic_interrupt(CPUState *env)

static void pic_irq_request(void *opaque, int irq, int level)
{
-    CPUState *env = opaque;
-    if (level && apic_accept_pic_intr(env))
-        cpu_interrupt(env, CPU_INTERRUPT_HARD);
+    CPUState *env = first_cpu;
+
+    if (!level)
+        return;
+
+    while (env) {
+        if (apic_accept_pic_intr(env))
+            apic_local_deliver(env, APIC_LINT0);
+        env = env->next_cpu;
+    }
}

/* PC cmos mappings */
@@ -845,7 +852,7 @@ static void pc_init1(int ram_size, int v
    if (linux_boot)
        load_linux(kernel_filename, initrd_filename, kernel_cmdline);

-    cpu_irq = qemu_allocate_irqs(pic_irq_request, first_cpu, 1);
+    cpu_irq = qemu_allocate_irqs(pic_irq_request, NULL, 1);
    i8259 = i8259_init(cpu_irq[0]);
    ferr_irq = i8259[13];

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);

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