[Qemu-devel] [RFC][PATCH] apic: Fix relocation

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

When the guest remaps an APIC by modifying MSR_IA32_APICBASE, we need to
update its mmio mapping. This is a bit tricky as multiple APICs might be
mapped to the same address. So walk through the full list to avoid
unmapping a region that is still in use.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

RFC as I did not yet have a chance to test actual relocation. Standard
OSes don't do this, otherwise we would have noticed this earlier.

 hw/apic.c |   38 +++++++++++++++++++++++++++++++++++++-
 hw/pc.c   |   10 ----------
 2 files changed, 37 insertions(+), 11 deletions(-)

diff --git a/hw/apic.c b/hw/apic.c
index 05a115f..b64af59 100644
--- a/hw/apic.c
+++ b/hw/apic.c
@@ -294,6 +294,40 @@ void apic_deliver_irq(uint8_t dest, uint8_t dest_mode,
                      trigger_mode);
 }
 
+static void apic_update_mapping(APICState *s)
+{
+    target_phys_addr_t new_addr;
+    bool overlap = false;
+    APICState *apic_iter;
+    int i;
+
+    for (i = 0; i < MAX_APICS; i++) {
+        apic_iter = local_apics[i];
+        if (!apic_iter || apic_iter == s) {
+            continue;
+        }
+        if ((apic_iter->apicbase & MSR_IA32_APICBASE_BASE) ==
+            s->busdev.mmio[0].addr) {
+            overlap = true;
+            break;
+        }
+    }
+    if (overlap) {
+        /*
+         * As APICs are pre-CPU devices, they may have identical base
+         * addresses. We must avoid unregistering an old io-region that is
+         * still in use by another APIC.
+         */
+        s->busdev.mmio[0].addr = (target_phys_addr_t)-1;
+    }
+    if (s->apicbase & MSR_IA32_APICBASE_ENABLE) {
+        new_addr = s->apicbase & MSR_IA32_APICBASE_BASE;
+    } else {
+        new_addr = (target_phys_addr_t)-1;
+    }
+    sysbus_mmio_map(&s->busdev, 0, new_addr);
+}
+
 void cpu_set_apic_base(DeviceState *d, uint64_t val)
 {
     APICState *s = DO_UPCAST(APICState, busdev.qdev, d);
@@ -302,7 +336,7 @@ void cpu_set_apic_base(DeviceState *d, uint64_t val)
 
     if (!s)
         return;
-    s->apicbase = (val & 0xfffff000) |
+    s->apicbase = (val & MSR_IA32_APICBASE_BASE) |
         (s->apicbase & (MSR_IA32_APICBASE_BSP | MSR_IA32_APICBASE_ENABLE));
     /* if disabled, cannot be enabled again */
     if (!(val & MSR_IA32_APICBASE_ENABLE)) {
@@ -310,6 +344,7 @@ void cpu_set_apic_base(DeviceState *d, uint64_t val)
         cpu_clear_apic_feature(s->cpu_env);
         s->spurious_vec &= ~APIC_SV_ENABLE;
     }
+    apic_update_mapping(s);
 }
 
 uint64_t cpu_get_apic_base(DeviceState *d)
@@ -948,6 +983,7 @@ static void apic_reset(DeviceState *d)
     bsp = cpu_is_bsp(s->cpu_env);
     s->apicbase = 0xfee00000 |
         (bsp ? MSR_IA32_APICBASE_BSP : 0) | MSR_IA32_APICBASE_ENABLE;
+    apic_update_mapping(s);
 
     apic_init_reset(d);
 
diff --git a/hw/pc.c b/hw/pc.c
index 4dfdc0b..294aa66 100644
--- a/hw/pc.c
+++ b/hw/pc.c
@@ -859,7 +859,6 @@ static DeviceState *apic_init(void *env, uint8_t apic_id)
 {
     DeviceState *dev;
     SysBusDevice *d;
-    static int apic_mapped;
 
     dev = qdev_create(NULL, "apic");
     qdev_prop_set_uint8(dev, "id", apic_id);
@@ -867,15 +866,6 @@ static DeviceState *apic_init(void *env, uint8_t apic_id)
     qdev_init_nofail(dev);
     d = sysbus_from_qdev(dev);
 
-    /* XXX: mapping more APICs at the same memory location */
-    if (apic_mapped == 0) {
-        /* NOTE: the APIC is directly connected to the CPU - it is not
-           on the global memory bus. */
-        /* XXX: what if the base changes? */
-        sysbus_mmio_map(d, 0, MSI_ADDR_BASE);
-        apic_mapped = 1;
-    }
-
     msix_supported = 1;
 
     return dev;
-- 
1.7.1