Re: [PATCH v7 1/2] i386: kvm: extend kvm_{get, put}_vcpu_events to support pending triple fault

[Paolo Bonzini]

On 9/23/22 09:33, Chenyi Qiang wrote:
> For the direct triple faults, i.e. hardware detected and KVM morphed
> to VM-Exit, KVM will never lose them. But for triple faults sythesized
> by KVM, e.g. the RSM path, if KVM exits to userspace before the request
> is serviced, userspace could migrate the VM and lose the triple fault.
>
> A new flag KVM_VCPUEVENT_VALID_TRIPLE_FAULT is defined to signal that
> the event.triple_fault_pending field contains a valid state if the
> KVM_CAP_X86_TRIPLE_FAULT_EVENT capability is enabled.

Note that you are not transmitting the field on migration.  You need
this on top:

diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index b97d182e28..d4124973ce 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -1739,7 +1739,7 @@ typedef struct CPUArchState {
     uint8_t has_error_code;
     uint8_t exception_has_payload;
     uint64_t exception_payload;
-    bool triple_fault_pending;
+    uint8_t triple_fault_pending;
     uint32_t ins_len;
     uint32_t sipi_vector;
     bool tsc_valid;
diff --git a/target/i386/machine.c b/target/i386/machine.c
index cecd476e98..310b125235 100644
--- a/target/i386/machine.c
+++ b/target/i386/machine.c
@@ -1562,6 +1562,25 @@ static const VMStateDescription vmstate_arch_lbr = {
     }
 };
 
+static bool triple_fault_needed(void *opaque)
+{
+    X86CPU *cpu = opaque;
+    CPUX86State *env = &cpu->env;
+
+    return env->triple_fault_pending;
+}
+
+static const VMStateDescription vmstate_triple_fault = {
+    .name = "cpu/triple_fault",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = triple_fault_needed,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT8(env.triple_fault_pending, X86CPU),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 const VMStateDescription vmstate_x86_cpu = {
     .name = "cpu",
     .version_id = 12,
@@ -1706,6 +1725,7 @@ const VMStateDescription vmstate_x86_cpu = {
         &vmstate_amx_xtile,
 #endif
         &vmstate_arch_lbr,
+        &vmstate_triple_fault,
         NULL
     }
 };