[Qemu-devel] [PATCH v4 2/2] target-i386: add support to migrate vcpu's TSC rate

[Haozhong Zhang]

This patch enables migrating vcpu's TSC rate. If KVM on the destination
machine supports TSC scaling, guest programs will observe a consistent
TSC rate across the migration.

If TSC scaling is not supported on the destination machine, the
migration will not be aborted and QEMU on the destination will not set
vcpu's TSC rate to the migrated value.

If vcpu's TSC rate specified by CPU option 'tsc-freq' on the destination
machine is inconsistent with the migrated TSC rate, the migration will
be aborted.

For backwards compatibility, the migration of vcpu's TSC rate is
disabled on pc-*-2.4 and older machine types.

Signed-off-by: Haozhong Zhang <address@hidden>
---
 hw/i386/pc.c          |  1 +
 hw/i386/pc_piix.c     |  1 +
 hw/i386/pc_q35.c      |  1 +
 include/hw/i386/pc.h  |  1 +
 target-i386/cpu.c     |  2 +-
 target-i386/cpu.h     |  1 +
 target-i386/kvm.c     | 26 ++++++++++++++++++++++++--
 target-i386/machine.c | 28 ++++++++++++++++++++++++++++
 8 files changed, 58 insertions(+), 3 deletions(-)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 0cb8afd..2f2fc93 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -1952,6 +1952,7 @@ static void pc_machine_class_init(ObjectClass *oc, void 
*data)
     HotplugHandlerClass *hc = HOTPLUG_HANDLER_CLASS(oc);
 
     pcmc->get_hotplug_handler = mc->get_hotplug_handler;
+    pcmc->save_tsc_khz = true;
     mc->get_hotplug_handler = pc_get_hotpug_handler;
     mc->cpu_index_to_socket_id = pc_cpu_index_to_socket_id;
     mc->default_boot_order = "cad";
diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index 07d0baa..7c5b0d2 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -489,6 +489,7 @@ static void pc_i440fx_2_4_machine_options(MachineClass *m)
     m->alias = NULL;
     m->is_default = 0;
     pcmc->broken_reserved_end = true;
+    pcmc->save_tsc_khz = false;
     SET_MACHINE_COMPAT(m, PC_COMPAT_2_4);
 }
 
diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index 0fdae09..fd8efe3 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -387,6 +387,7 @@ static void pc_q35_2_4_machine_options(MachineClass *m)
     m->hw_version = "2.4.0";
     m->alias = NULL;
     pcmc->broken_reserved_end = true;
+    pcmc->save_tsc_khz = false;
     SET_MACHINE_COMPAT(m, PC_COMPAT_2_4);
 }
 
diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
index 4bbc0ff..fea0f28 100644
--- a/include/hw/i386/pc.h
+++ b/include/hw/i386/pc.h
@@ -60,6 +60,7 @@ struct PCMachineClass {
 
     /*< public >*/
     bool broken_reserved_end;
+    bool save_tsc_khz;
     HotplugHandler *(*get_hotplug_handler)(MachineState *machine,
                                            DeviceState *dev);
 };
diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index e5f1c5b..98c6a4c 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -1724,7 +1724,7 @@ static void x86_cpuid_set_tsc_freq(Object *obj, Visitor 
*v, void *opaque,
         return;
     }
 
-    cpu->env.tsc_khz = value / 1000;
+    cpu->env.tsc_khz = cpu->env.user_tsc_khz = value / 1000;
 }
 
 static void x86_cpuid_get_apic_id(Object *obj, Visitor *v, void *opaque,
diff --git a/target-i386/cpu.h b/target-i386/cpu.h
index fc4a605..1ad1da8 100644
--- a/target-i386/cpu.h
+++ b/target-i386/cpu.h
@@ -973,6 +973,7 @@ typedef struct CPUX86State {
     uint32_t sipi_vector;
     bool tsc_valid;
     int64_t tsc_khz;
+    int64_t user_tsc_khz;
     void *kvm_xsave_buf;
 
     uint64_t mcg_cap;
diff --git a/target-i386/kvm.c b/target-i386/kvm.c
index 9084b29..8448248 100644
--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -2334,8 +2334,30 @@ static void kvm_arch_set_tsc_khz(CPUState *cs)
     int r;
 
     /*
-     * If no user-specified TSC frequency is present, we will try to
-     * set env->tsc_khz to the value used by KVM.
+     * For other cases of env->tsc_khz and env->user_tsc_khz:
+     *
+     * - We have eliminated all cases that satisfy
+     *       env->tsc_khz && env->user_tsc_khz &&
+     *       env->tsc_khz != env->user_tsc_khz
+     *   in cpu_post_load().
+     *
+     * - If env->user_tsc_khz is not zero, then it must be equal to
+     *   env->tsc_khz (if the latter is not zero) and has been set in
+     *   kvm_arch_init_vcpu().
+     */
+    if (env->tsc_khz && !env->user_tsc_khz) {
+        r = kvm_check_extension(cs->kvm_state, KVM_CAP_TSC_CONTROL) ?
+            kvm_vcpu_ioctl(cs, KVM_SET_TSC_KHZ, env->tsc_khz) : -ENOTSUP;
+        if (r < 0) {
+            error_report("warning: TSC frequency mismatch between VM and host, 
"
+                         "and TSC scaling unavailable");
+        }
+    }
+
+    /*
+     * If neither the user-specified TSC frequency nor the migrated
+     * TSC frequency is present, we will try to set env->tsc_khz
+     * to the value used by KVM.
      */
     if (!env->tsc_khz) {
         r = kvm_check_extension(cs->kvm_state, KVM_CAP_GET_TSC_KHZ) ?
diff --git a/target-i386/machine.c b/target-i386/machine.c
index a18e16e..eb062d2 100644
--- a/target-i386/machine.c
+++ b/target-i386/machine.c
@@ -331,6 +331,13 @@ static int cpu_post_load(void *opaque, int version_id)
     CPUX86State *env = &cpu->env;
     int i;
 
+    if (env->tsc_khz && env->user_tsc_khz &&
+        env->tsc_khz != env->user_tsc_khz) {
+        fprintf(stderr, "Mismatch between user-specified TSC frequency and "
+                "migrated TSC frequency");
+        return -1;
+    }
+
     /*
      * Real mode guest segments register DPL should be zero.
      * Older KVM version were setting it wrongly.
@@ -775,6 +782,26 @@ static const VMStateDescription vmstate_xss = {
     }
 };
 
+static bool tsc_khz_needed(void *opaque)
+{
+    X86CPU *cpu = opaque;
+    CPUX86State *env = &cpu->env;
+    MachineClass *mc = MACHINE_GET_CLASS(qdev_get_machine());
+    PCMachineClass *pcmc = PC_MACHINE_CLASS(mc);
+    return env->tsc_khz && pcmc->save_tsc_khz;
+}
+
+static const VMStateDescription vmstate_tsc_khz = {
+    .name = "cpu/tsc_khz",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .needed = tsc_khz_needed,
+    .fields = (VMStateField[]) {
+        VMSTATE_INT64(env.tsc_khz, X86CPU),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 VMStateDescription vmstate_x86_cpu = {
     .name = "cpu",
     .version_id = 12,
@@ -895,6 +922,7 @@ VMStateDescription vmstate_x86_cpu = {
         &vmstate_msr_hyperv_runtime,
         &vmstate_avx512,
         &vmstate_xss,
+        &vmstate_tsc_khz,
         NULL
     }
 };
-- 
2.4.8