[Qemu-devel] [PATCH v3] x86: ioapic: add support for explicit EOI

[Peter Xu <peterx@redhat.com>]

Some old Linux kernels (upstream before v4.0), or any released RHEL
kernels has problem in sending APIC EOI when IR is enabled. Meanwhile,
many of them only support explicit EOI for IOAPIC, which is only
introduced in IOAPIC version 0x20. This patch provide a way to boost
QEMU IOAPIC to version 0x20, in order for QEMU to correctly receive EOI
messages.

Without boosting IOAPIC version to 0x20, kernels before commit d32932d
("x86/irq: Convert IOAPIC to use hierarchical irqdomain interfaces")
will have trouble enabling both IR and level-triggered interrupt devices
(like e1000).

To upgrade IOAPIC to version 0x20, we need to specify:

  -global ioapic.version=0x20

To be compatible with old systems, 0x11 will still be the default IOAPIC
version. Here 0x11 and 0x20 are the only versions to be supported.

One thing to mention: this patch only applies to emulated IOAPIC. It
does not affect kernel IOAPIC behavior.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 hw/intc/ioapic.c                  | 22 +++++++++++++++++++++-
 include/hw/i386/ioapic_internal.h |  4 ++--
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/hw/intc/ioapic.c b/hw/intc/ioapic.c
index 2d3282a..e8568d2 100644
--- a/hw/intc/ioapic.c
+++ b/hw/intc/ioapic.c
@@ -21,6 +21,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu/error-report.h"
 #include "monitor/monitor.h"
 #include "hw/hw.h"
 #include "hw/i386/pc.h"
@@ -265,7 +266,7 @@ ioapic_mem_read(void *opaque, hwaddr addr, unsigned int size)
             val = s->id << IOAPIC_ID_SHIFT;
             break;
         case IOAPIC_REG_VER:
-            val = IOAPIC_VERSION |
+            val = s->version |
                 ((IOAPIC_NUM_PINS - 1) << IOAPIC_VER_ENTRIES_SHIFT);
             break;
         default:
@@ -354,6 +355,13 @@ ioapic_mem_write(void *opaque, hwaddr addr, uint64_t val,
             }
         }
         break;
+    case IOAPIC_EOI:
+        /* Explicit EOI is only supported for IOAPIC version 0x20 */
+        if (size != 4 || s->version != 0x20) {
+            break;
+        }
+        ioapic_eoi_broadcast(val);
+        break;
     }
 
     ioapic_update_kvm_routes(s);
@@ -387,6 +395,12 @@ static void ioapic_realize(DeviceState *dev, Error **errp)
 {
     IOAPICCommonState *s = IOAPIC_COMMON(dev);
 
+    if (s->version != 0x11 && s->version != 0x20) {
+        error_report("IOAPIC only supports version 0x11 or 0x20 "
+                     "(default: 0x11).");
+        exit(1);
+    }
+
     memory_region_init_io(&s->io_memory, OBJECT(s), &ioapic_io_ops, s,
                           "ioapic", 0x1000);
 
@@ -397,6 +411,11 @@ static void ioapic_realize(DeviceState *dev, Error **errp)
     qemu_add_machine_init_done_notifier(&s->machine_done);
 }
 
+static Property ioapic_properties[] = {
+    DEFINE_PROP_UINT8("version", IOAPICCommonState, version, 0x11),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
 static void ioapic_class_init(ObjectClass *klass, void *data)
 {
     IOAPICCommonClass *k = IOAPIC_COMMON_CLASS(klass);
@@ -404,6 +423,7 @@ static void ioapic_class_init(ObjectClass *klass, void *data)
 
     k->realize = ioapic_realize;
     dc->reset = ioapic_reset_common;
+    dc->props = ioapic_properties;
 }
 
 static const TypeInfo ioapic_info = {
diff --git a/include/hw/i386/ioapic_internal.h b/include/hw/i386/ioapic_internal.h
index d89ea1b..a11d86d 100644
--- a/include/hw/i386/ioapic_internal.h
+++ b/include/hw/i386/ioapic_internal.h
@@ -29,8 +29,6 @@
 
 #define MAX_IOAPICS                     1
 
-#define IOAPIC_VERSION                  0x11
-
 #define IOAPIC_LVT_DEST_SHIFT           56
 #define IOAPIC_LVT_DEST_IDX_SHIFT       48
 #define IOAPIC_LVT_MASKED_SHIFT         16
@@ -71,6 +69,7 @@
 
 #define IOAPIC_IOREGSEL                 0x00
 #define IOAPIC_IOWIN                    0x10
+#define IOAPIC_EOI                      0x40
 
 #define IOAPIC_REG_ID                   0x00
 #define IOAPIC_REG_VER                  0x01
@@ -109,6 +108,7 @@ struct IOAPICCommonState {
     uint32_t irr;
     uint64_t ioredtbl[IOAPIC_NUM_PINS];
     Notifier machine_done;
+    uint8_t version;
 };
 
 void ioapic_reset_common(DeviceState *dev);
-- 
2.7.4