target-i386: Add support to migrate vcpu's TSC rate

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-*-2.5 and older machine types.

Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
[ehabkost: Rewrote comment at kvm_arch_put_registers()]
[ehabkost: Moved compat code to pc-2.5]
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

4 files changed, 41 insertions, 1 deletions

diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index 69880b7..d3f8a4e 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -1728,7 +1728,7 @@ 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 77e62b2..28cbaf5 100644
--- a/target-i386/cpu.h
+++ b/target-i386/cpu.h
@@ -978,6 +978,7 @@ typedef struct CPUX86State {
     uint32_t sipi_vector;
     bool tsc_valid;
     int64_t tsc_khz;
+    int64_t user_tsc_khz; /* for sanity check only */
     void *kvm_xsave_buf;
 
     uint64_t mcg_cap;
diff --git a/target-i386/kvm.c b/target-i386/kvm.c
index 23d6b86..419bb18 100644
--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -2507,6 +2507,15 @@ int kvm_arch_put_registers(CPUState *cpu, int level)
         }
     }
 
+    if (level == KVM_PUT_FULL_STATE) {
+        /* We don't check for kvm_arch_set_tsc_khz() errors here,
+         * because TSC frequency mismatch shouldn't abort migration,
+         * unless the user explicitly asked for a more strict TSC
+         * setting (e.g. using an explicit "tsc-freq" option).
+         */
+        kvm_arch_set_tsc_khz(cpu);
+    }
+
     ret = kvm_getput_regs(x86_cpu, 1);
     if (ret < 0) {
         return ret;
diff --git a/target-i386/machine.c b/target-i386/machine.c
index 4d80288..0d381ac 100644
--- a/target-i386/machine.c
+++ b/target-i386/machine.c
@@ -6,6 +6,8 @@
 #include "cpu.h"
 #include "sysemu/kvm.h"
 
+#include "qemu/error-report.h"
+
 static const VMStateDescription vmstate_segment = {
     .name = "segment",
     .version_id = 1,
@@ -331,6 +333,13 @@ 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) {
+        error_report("Mismatch between user-specified TSC frequency and "
+                     "migrated TSC frequency");
+        return -EINVAL;
+    }
+
     /*
      * Real mode guest segments register DPL should be zero.
      * Older KVM version were setting it wrongly.
@@ -839,6 +848,26 @@ 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,
@@ -961,6 +990,7 @@ VMStateDescription vmstate_x86_cpu = {
         &vmstate_msr_hyperv_stimer,
         &vmstate_avx512,
         &vmstate_xss,
+        &vmstate_tsc_khz,
         NULL
     }
 };