Re: [Qemu-devel] [PATCH 06/12] kvmvapic: fixing loading vmstate

[Paolo Bonzini]

Il 27/08/2014 15:03, Pavel Dovgaluk ha scritto:
>> > Hmm, probably not.  The bug would not be other timers accessing the
>> > APIC, because that would also call apic_sync_vapic and the only effect
>> > would be an extra useless synchronization.  The bug would happen if the
>> > APIC is accessed by the CPU before the timer has the occasion to run.
> Sorry, but I don't understand which problem we will solve with 
> apic_sync_vapic.

In KVM mode, it is not a problem to call apic_enable_vapic before APIC
state is loaded; all vapic processing is delayed anyway to after the
VCPUs are started.

In TCG mode, apic_enable_vapic calls apic_sync_vapic.

Taking inspiration from what KVM does, the fix could be even simpler
than a change state handler.  run_on_cpu functions do not run while the
VM is stopped, so the following should work:

diff --git a/hw/intc/apic_common.c b/hw/intc/apic_common.c
index ce3d903..81d1ad7 100644
--- a/hw/intc/apic_common.c
+++ b/hw/intc/apic_common.c
@@ -91,13 +91,20 @@ void apic_enable_tpr_access_reporting(DeviceState
*dev, bool enable)
     }
 }

+static void do_apic_enable_vapic(void *data)
+{
+    APICCommonState *s = APIC_COMMON(data);
+    APICCommonClass *info = APIC_COMMON_GET_CLASS(s);
+
+    info->vapic_base_update(s);
+}
+
 void apic_enable_vapic(DeviceState *dev, hwaddr paddr)
 {
     APICCommonState *s = APIC_COMMON(dev);
-    APICCommonClass *info = APIC_COMMON_GET_CLASS(s);

     s->vapic_paddr = paddr;
-    info->vapic_base_update(s);
+    run_on_cpu(CPU(s->cpu), do_apic_enable_vapic, s);
 }

 void apic_handle_tpr_access_report(DeviceState *dev, target_ulong ip,

> All fields that were added to vmstate are not affected by this function.

The sipi_vector and wait_for_sipi parts of this patch are okay.  You
should split those in a separate patch.

Paolo