[Qemu-devel] [PATCH 3/3] kvm-all: notice KVM of vcpu's TSC rate after migration

[Haozhong Zhang <haozhong.zhang@intel.com>]

When a vcpu is created in KVM, its TSC rate is initially identical to
the host TSC rate. If its state is migrated to a vcpu on another
machine (target machine) which may uses a different host TSC rate, QEMU
on the target machine should notice KVM of the migrated vcpu's TSC
rate. In case that KVM on the target machine supports TSC scaling, guest
programs running on the migrated vcpu will observe the same TSC rate
before and after the migration.

Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
---
 kvm-all.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/kvm-all.c b/kvm-all.c
index 0be4615..e8de038 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -1769,6 +1769,19 @@ void kvm_cpu_synchronize_post_reset(CPUState *cpu)
 static void do_kvm_cpu_synchronize_post_init(void *arg)
 {
     CPUState *cpu = arg;
+    CPUX86State *env = &X86_CPU(cpu)->env;
+    int r;
+
+    /*
+     * XXX: KVM_SET_TSC_KHZ must be done before kvm_arch_put_registers().
+     */
+    r = kvm_check_extension(cpu->kvm_state, KVM_CAP_TSC_CONTROL);
+    if (r && env->tsc_khz) {
+        r = kvm_vcpu_ioctl(cpu, KVM_SET_TSC_KHZ, env->tsc_khz);
+        if (r < 0) {
+            fprintf(stderr, "KVM_SET_TSC_KHZ failed\n");
+        }
+    }
 
     kvm_arch_put_registers(cpu, KVM_PUT_FULL_STATE);
     cpu->kvm_vcpu_dirty = false;
-- 
2.4.8