[Qemu-devel] [PATCH v2] pc: Fix and clean up PIC-to-APIC IRQ path

[Jan Kiszka]

The master PIC is connected to the LINTIN0 of the APICs. As the APIC
currently does not track the state of that line, we have to ask the PIC
to reinject its IRQ after the CPU picked up an event from the APIC.

This introduces pic_get_output to read the master PIC IRQ line state
without changing it. The APIC uses this function to decide if a PIC IRQ
should be reinjected on apic_update_irq. This reflects better how the
real hardware works.

The patch fixes some failures of the kvm unit tests apic and eventinj by
allowing to enable the proper CPU IRQ deassertion when the guest masks
some pending IRQs at PIC level.

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

Changes in v2:
 - Avoid adding pic_level to the APIC state, obtain PIC output via
   pic_get_level instead
 - Do not reassert PIC interrupt if APIC is not accepting it
 - Use apic_deliver_pic_intr for reassertion to ensure correct
   processing

This is not as nice as the previous version /wrt the interaction of PIC
and APIC. But it avoids breaking the APIC vmstate for the sake of
internal changes, also keeping it compatible with the upcoming KVM
in-kernel APIC (that allows no easy pic_level state extraction). The
interconnection between PIC and APIC may look nicer in the future with
QOM. And in the end this just reflects the "beauty" of the x86
architecture.

 hw/apic.c  |    4 ++++
 hw/i8259.c |   15 +++++++--------
 hw/pc.c    |    3 ---
 hw/pc.h    |    2 +-
 4 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/hw/apic.c b/hw/apic.c
index d8f56c8..8289eef 100644
--- a/hw/apic.c
+++ b/hw/apic.c
@@ -23,6 +23,7 @@
 #include "host-utils.h"
 #include "sysbus.h"
 #include "trace.h"
+#include "pc.h"
 
 /* APIC Local Vector Table */
 #define APIC_LVT_TIMER   0
@@ -399,6 +400,9 @@ static void apic_update_irq(APICState *s)
     }
     if (apic_irq_pending(s) > 0) {
         cpu_interrupt(s->cpu_env, CPU_INTERRUPT_HARD);
+    } else if (apic_accept_pic_intr(&s->busdev.qdev) &&
+               pic_get_output(isa_pic)) {
+        apic_deliver_pic_intr(&s->busdev.qdev, 1);
     }
 }
 
diff --git a/hw/i8259.c b/hw/i8259.c
index c0b96ab..5498e5b 100644
--- a/hw/i8259.c
+++ b/hw/i8259.c
@@ -144,8 +144,7 @@ static int pic_get_irq(PicState *s)
 
 /* raise irq to CPU if necessary. must be called every time the active
    irq may change */
-/* XXX: should not export it, but it is needed for an APIC kludge */
-void pic_update_irq(PicState2 *s)
+static void pic_update_irq(PicState2 *s)
 {
     int irq2, irq;
 
@@ -172,14 +171,9 @@ void pic_update_irq(PicState2 *s)
         printf("pic: cpu_interrupt\n");
 #endif
         qemu_irq_raise(s->parent_irq);
-    }
-
-/* all targets should do this rather than acking the IRQ in the cpu */
-#if defined(TARGET_MIPS) || defined(TARGET_PPC) || defined(TARGET_ALPHA)
-    else {
+    } else {
         qemu_irq_lower(s->parent_irq);
     }
-#endif
 }
 
 #ifdef DEBUG_IRQ_LATENCY
@@ -436,6 +430,11 @@ uint32_t pic_intack_read(PicState2 *s)
     return ret;
 }
 
+int pic_get_output(PicState2 *s)
+{
+    return (pic_get_irq(&s->pics[0]) >= 0);
+}
+
 static void elcr_ioport_write(void *opaque, uint32_t addr, uint32_t val)
 {
     PicState *s = opaque;
diff --git a/hw/pc.c b/hw/pc.c
index 263fb1a..b7b5d6f 100644
--- a/hw/pc.c
+++ b/hw/pc.c
@@ -156,9 +156,6 @@ int cpu_get_pic_interrupt(CPUState *env)
 
     intno = apic_get_interrupt(env->apic_state);
     if (intno >= 0) {
-        /* set irq request if a PIC irq is still pending */
-        /* XXX: improve that */
-        pic_update_irq(isa_pic);
         return intno;
     }
     /* read the irq from the PIC */
diff --git a/hw/pc.h b/hw/pc.h
index dae736e..958c77d 100644
--- a/hw/pc.h
+++ b/hw/pc.h
@@ -65,7 +65,7 @@ void pic_set_irq(int irq, int level);
 void pic_set_irq_new(void *opaque, int irq, int level);
 qemu_irq *i8259_init(qemu_irq parent_irq);
 int pic_read_irq(PicState2 *s);
-void pic_update_irq(PicState2 *s);
+int pic_get_output(PicState2 *s);
 uint32_t pic_intack_read(PicState2 *s);
 void pic_info(Monitor *mon);
 void irq_info(Monitor *mon);