Peter Maydell [off-list ref] writes:

On 26 February 2015 at 01:02, Alex Benn?e [off-list ref] wrote:

quoted

This adds the saving and restore of the current Multi-Processing state
of the machine. While the KVM_GET/SET_MP_STATE API exposes a number of
potential states for x86 we only use two for ARM. Either the process is
running or not.

By this you mean "is the CPU in the PSCI powered down state or not",
right?

From the vcpu's perspective it is either running or not. However it is

the same mechanism that is used when PSCI_0_2_FN_CPU_OFF is passed the
VM, internally setting vcpu->arch.paused.

quoted

Signed-off-by: Alex Benn?e <redacted>

diff --git a/target-arm/kvm.c b/target-arm/kvm.c
index 23cefe9..8732854 100644
--- a/target-arm/kvm.c
+++ b/target-arm/kvm.c

@@ -25,6 +25,7 @@
 #include "hw/arm/arm.h"

 const KVMCapabilityInfo kvm_arch_required_capabilities[] = {
+    KVM_CAP_INFO(MP_STATE),

Does this really want to be a required cap? I haven't checked,
but assuming 'required' means what it says this presumably
means we'll stop working on host kernels we previously ran
fine on (even if migration didn't work there).

You are right, I'll move the CAP check to the kvm_enabled() leg of
get/set functions.

quoted

     KVM_CAP_LAST_INFO
 };

diff --git a/target-arm/machine.c b/target-arm/machine.c
index 9446e5a..70b1bc4 100644
--- a/target-arm/machine.c
+++ b/target-arm/machine.c

@@ -161,6 +161,34 @@ static const VMStateInfo vmstate_cpsr = {
     .put = put_cpsr,
 };

+#if defined CONFIG_KVM
+static int get_mpstate(QEMUFile *f, void *opaque, size_t size)
+{
+    ARMCPU *cpu = opaque;
+    struct kvm_mp_state mp_state = { .mp_state =  qemu_get_be32(f)};
+    return kvm_vcpu_ioctl(CPU(cpu), KVM_SET_MP_STATE, &mp_state);
+}

Won't this break if you're running a QEMU built with KVM
support in TCG mode on an aarch64 host?

In any case, for that configuration we should be migrating the
TCG cpu->powered_off flag, which is where we keep the PSCI
power state for TCG.

Yeah, I'll make the access functions aware of the mode. In itself it
won't enable KVM<->TCG migration though!

quoted

+
+static void put_mpstate(QEMUFile *f, void *opaque, size_t size)
+{
+    ARMCPU *cpu = opaque;
+    struct kvm_mp_state mp_state;
+    int ret = kvm_vcpu_ioctl(CPU(cpu), KVM_GET_MP_STATE, &mp_state);
+    if (ret) {
+        fprintf(stderr, "%s: failed to get MP_STATE %d/%s\n",
+                __func__, ret, strerror(ret));
+        abort();
+    }
+    qemu_put_be32(f, mp_state.mp_state);
+}
+
+static const VMStateInfo vmstate_mpstate = {
+    .name = "mpstate",
+    .get = get_mpstate,
+    .put = put_mpstate,
+};
+#endif
+
 static void cpu_pre_save(void *opaque)
 {
     ARMCPU *cpu = opaque;

@@ -244,6 +272,16 @@ const VMStateDescription vmstate_arm_cpu = {
         VMSTATE_UINT32_ARRAY(env.regs, ARMCPU, 16),
         VMSTATE_UINT64_ARRAY(env.xregs, ARMCPU, 32),
         VMSTATE_UINT64(env.pc, ARMCPU),
+#if defined CONFIG_KVM
+        {
+            .name = "mp_state",
+            .version_id = 0,
+            .size = sizeof(uint32_t),
+            .info = &vmstate_mpstate,
+            .flags = VMS_SINGLE,
+            .offset = 0,
+        },
+#endif

This means the migration format will be different on different
build configurations, which seems like a really bad idea.

Have you considered having the KVM state sync functions just
sync the kernel's MP state into cpu->powered_off, and then
migrating that flag here unconditionally?

I was looking at using:

  .field_exists = mpstate_valid

for the field. If we have the field in the migration stream and the
kernel doesn't have the capability to set the state we need to fail hard
right?

quoted

         {
             .name = "cpsr",
             .version_id = 0,
--
2.3.0

-- PMM

-- 
Alex Benn?e