[RFC PATCH v2 35/44] ioapic: add property to disable level interrupt

[isaku . yamahata]

From: Isaku Yamahata <isaku.yamahata@intel.com>

According to TDX module spec version 344425-002US [1], VMM can inject
virtual interrupt only via posted interrupt and VMM can't get TDEXIT on
guest EOI to virtual x2APIC.  Because posted interrupt is edge-trigger and
VMM needs to hook guest EOI to re-inject level-triggered interrupt if the
level still active, level-trigger isn't supported for TD Guest VM.

Prevent trigger mode from setting to be level trigger with warning.
Without this guard, qemu can result in unexpected behavior later.

[1] 
https://software.intel.com/content/dam/develop/external/us/en/documents/tdx-module-1eas-v0.85.039.pdf

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
---
 hw/intc/ioapic.c                  | 20 ++++++++++++++++++++
 hw/intc/ioapic_common.c           | 27 +++++++++++++++++++++++++++
 include/hw/i386/ioapic_internal.h |  1 +
 3 files changed, 48 insertions(+)

diff --git a/hw/intc/ioapic.c b/hw/intc/ioapic.c
index 264262959d..6d61744961 100644
--- a/hw/intc/ioapic.c
+++ b/hw/intc/ioapic.c
@@ -364,6 +364,23 @@ ioapic_fix_edge_remote_irr(uint64_t *entry)
     }
 }
 
+static inline void
+ioapic_fix_level_trigger_unsupported(uint64_t *entry)
+{
+    if ((*entry & IOAPIC_LVT_TRIGGER_MODE) !=
+        IOAPIC_TRIGGER_EDGE << IOAPIC_LVT_TRIGGER_MODE_SHIFT) {
+        /*
+         * ignore a request for level trigger because
+         * level trigger requires eoi intercept to re-inject
+         * interrupt when the level is still active.
+         */
+        warn_report_once("attempting to set level-trigger mode "
+                         "while eoi intercept isn't supported");
+        *entry &= ~IOAPIC_LVT_TRIGGER_MODE;
+        *entry |= IOAPIC_TRIGGER_EDGE << IOAPIC_LVT_TRIGGER_MODE_SHIFT;
+    }
+}
+
 static void
 ioapic_mem_write(void *opaque, hwaddr addr, uint64_t val,
                  unsigned int size)
@@ -404,6 +421,9 @@ ioapic_mem_write(void *opaque, hwaddr addr, uint64_t val,
                 s->ioredtbl[index] &= IOAPIC_RW_BITS;
                 s->ioredtbl[index] |= ro_bits;
                 s->irq_eoi[index] = 0;
+                if (s->level_trigger_unsupported) {
+                    ioapic_fix_level_trigger_unsupported(&s->ioredtbl[index]);
+                }
                 ioapic_fix_edge_remote_irr(&s->ioredtbl[index]);
                 ioapic_service(s);
             }
diff --git a/hw/intc/ioapic_common.c b/hw/intc/ioapic_common.c
index 3cccfc1556..07ee142470 100644
--- a/hw/intc/ioapic_common.c
+++ b/hw/intc/ioapic_common.c
@@ -150,6 +150,32 @@ static int ioapic_dispatch_post_load(void *opaque, int 
version_id)
     return 0;
 }
 
+static bool ioapic_common_get_level_trigger_unsupported(Object *obj,
+                                                        Error **errp)
+{
+    IOAPICCommonState *s = IOAPIC_COMMON(obj);
+    return s->level_trigger_unsupported;
+}
+
+static void ioapic_common_set_level_trigger_unsupported(Object *obj, bool 
value,
+                                                       Error **errp)
+{
+    DeviceState *dev = DEVICE(obj);
+    IOAPICCommonState *s = IOAPIC_COMMON(obj);
+    /* only disabling before realize is allowed */
+    assert(!dev->realized);
+    assert(!s->level_trigger_unsupported);
+    s->level_trigger_unsupported = value;
+}
+
+static void ioapic_common_init(Object *obj)
+{
+    object_property_add_bool(obj, "level_trigger_unsupported",
+                             ioapic_common_get_level_trigger_unsupported,
+                             ioapic_common_set_level_trigger_unsupported);
+
+}
+
 static void ioapic_common_realize(DeviceState *dev, Error **errp)
 {
     IOAPICCommonState *s = IOAPIC_COMMON(dev);
@@ -207,6 +233,7 @@ static const TypeInfo ioapic_common_type = {
     .name = TYPE_IOAPIC_COMMON,
     .parent = TYPE_SYS_BUS_DEVICE,
     .instance_size = sizeof(IOAPICCommonState),
+    .instance_init = ioapic_common_init,
     .class_size = sizeof(IOAPICCommonClass),
     .class_init = ioapic_common_class_init,
     .abstract = true,
diff --git a/include/hw/i386/ioapic_internal.h 
b/include/hw/i386/ioapic_internal.h
index 021e715f11..20f2fc7897 100644
--- a/include/hw/i386/ioapic_internal.h
+++ b/include/hw/i386/ioapic_internal.h
@@ -103,6 +103,7 @@ struct IOAPICCommonState {
     uint32_t irr;
     uint64_t ioredtbl[IOAPIC_NUM_PINS];
     Notifier machine_done;
+    bool level_trigger_unsupported;
     uint8_t version;
     uint64_t irq_count[IOAPIC_NUM_PINS];
     int irq_level[IOAPIC_NUM_PINS];
-- 
2.25.1