[PATCH v2] hyperv: fix SynIC SINT assertion failure on guest reset

[Maciej S. Szmigiero]

From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>

Resetting a guest that has Hyper-V VMBus support enabled triggers a QEMU
assertion failure:
hw/hyperv/hyperv.c:131: synic_reset: Assertion 
`QLIST_EMPTY(&synic->sint_routes)' failed.

This happens both on normal guest reboot or when using "system_reset" HMP
command.

The failing assertion was introduced by commit 64ddecc88bcf ("hyperv: SControl 
is optional to enable SynIc")
to catch dangling SINT routes on SynIC reset.

The root cause of this problem is that the SynIC itself is reset before
devices using SINT routes have chance to clean up these routes.

Since there seems to be no existing mechanism to force reset callbacks (or
methods) to be executed in specific order let's use a similar method that
is already used to reset another interrupt controller (APIC) after devices
have been reset - by invoking the SynIC reset from the machine reset
handler via a new x86_cpu_after_reset() function co-located with
the existing x86_cpu_reset() in target/i386/cpu.c.

Fixes: 64ddecc88bcf ("hyperv: SControl is optional to enable SynIc") # exposed 
the bug
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
---

Changes from v1:
Directly call x86_cpu_after_reset() from pc_machine_reset() instead of
adding a new "after_reset" X86 CPU class method.

 hw/i386/pc.c               |  3 +++
 target/i386/cpu.c          |  9 +++++++++
 target/i386/cpu.h          |  2 ++
 target/i386/kvm/hyperv.c   |  4 ++++
 target/i386/kvm/kvm.c      | 24 +++++++++++++++++-------
 target/i386/kvm/kvm_i386.h |  1 +
 6 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 566accf7e6..736a4f34b0 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -92,6 +92,7 @@
 #include "hw/virtio/virtio-mem-pci.h"
 #include "hw/mem/memory-device.h"
 #include "sysemu/replay.h"
+#include "target/i386/cpu.h"
 #include "qapi/qmp/qerror.h"
 #include "e820_memory_layout.h"
 #include "fw_cfg.h"
@@ -1859,6 +1860,8 @@ static void pc_machine_reset(MachineState *machine)
     CPU_FOREACH(cs) {
         cpu = X86_CPU(cs);
 
+        x86_cpu_after_reset(cpu);
+
         if (cpu->apic_state) {
             device_legacy_reset(cpu->apic_state);
         }
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 1db1278a59..4ea605c3b0 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -6034,6 +6034,15 @@ static void x86_cpu_reset(DeviceState *dev)
 #endif
 }
 
+void x86_cpu_after_reset(X86CPU *cpu)
+{
+#ifndef CONFIG_USER_ONLY
+    if (kvm_enabled()) {
+        kvm_arch_after_reset_vcpu(cpu);
+    }
+#endif
+}
+
 static void mce_init(X86CPU *cpu)
 {
     CPUX86State *cenv = &cpu->env;
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 82004b65b9..c67d98e1a9 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -2079,6 +2079,8 @@ typedef struct PropValue {
 } PropValue;
 void x86_cpu_apply_props(X86CPU *cpu, PropValue *props);
 
+void x86_cpu_after_reset(X86CPU *cpu);
+
 uint32_t cpu_x86_virtual_addr_width(CPUX86State *env);
 
 /* cpu.c other functions (cpuid) */
diff --git a/target/i386/kvm/hyperv.c b/target/i386/kvm/hyperv.c
index 9026ef3a81..e3ac978648 100644
--- a/target/i386/kvm/hyperv.c
+++ b/target/i386/kvm/hyperv.c
@@ -23,6 +23,10 @@ int hyperv_x86_synic_add(X86CPU *cpu)
     return 0;
 }
 
+/*
+ * All devices possibly using SynIC have to be reset before calling this to let
+ * them remove their SINT routes first.
+ */
 void hyperv_x86_synic_reset(X86CPU *cpu)
 {
     hyperv_synic_reset(CPU(cpu));
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index a1fd1f5379..774484c588 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -2203,20 +2203,30 @@ void kvm_arch_reset_vcpu(X86CPU *cpu)
         env->mp_state = KVM_MP_STATE_RUNNABLE;
     }
 
+    /* enabled by default */
+    env->poll_control_msr = 1;
+
+    kvm_init_nested_state(env);
+
+    sev_es_set_reset_vector(CPU(cpu));
+}
+
+void kvm_arch_after_reset_vcpu(X86CPU *cpu)
+{
+    CPUX86State *env = &cpu->env;
+    int i;
+
+    /*
+     * Reset SynIC after all other devices have been reset to let them remove
+     * their SINT routes first.
+     */
     if (hyperv_feat_enabled(cpu, HYPERV_FEAT_SYNIC)) {
-        int i;
         for (i = 0; i < ARRAY_SIZE(env->msr_hv_synic_sint); i++) {
             env->msr_hv_synic_sint[i] = HV_SINT_MASKED;
         }
 
         hyperv_x86_synic_reset(cpu);
     }
-    /* enabled by default */
-    env->poll_control_msr = 1;
-
-    kvm_init_nested_state(env);
-
-    sev_es_set_reset_vector(CPU(cpu));
 }
 
 void kvm_arch_do_init_vcpu(X86CPU *cpu)
diff --git a/target/i386/kvm/kvm_i386.h b/target/i386/kvm/kvm_i386.h
index 4124912c20..096a5dd781 100644
--- a/target/i386/kvm/kvm_i386.h
+++ b/target/i386/kvm/kvm_i386.h
@@ -38,6 +38,7 @@ bool kvm_has_adjust_clock_stable(void);
 bool kvm_has_exception_payload(void);
 void kvm_synchronize_all_tsc(void);
 void kvm_arch_reset_vcpu(X86CPU *cs);
+void kvm_arch_after_reset_vcpu(X86CPU *cpu);
 void kvm_arch_do_init_vcpu(X86CPU *cs);
 
 void kvm_put_apicbase(X86CPU *cpu, uint64_t value);