commit 384331a61a8ca42f32516ced20cb52470c5f6f57
author Marcelo Tosatti <mtosatti@redhat.com> Thu Oct 21 13:35:03 2010 -0200
committer Marcelo Tosatti <mtosatti@redhat.com> Thu Oct 21 13:37:40 2010 -0200
tree f64c77db9ac9df9b4afc06ff1f2d75fa93bb2a48
parent 75b10c43365e2a9cab5398f31b96a463b0d57eff

kvm: writeback SMP TSCs on migration only

commit 6389c45441269baa2873e6feafebd17105ddeaf6
Author: Jan Kiszka <jan.kiszka@siemens.com>
Date:   Mon Mar 1 18:17:26 2010 +0100

    qemu-kvm: Cleanup/fix TSC and PV clock writeback

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

target-i386/kvm.c

diff --git a/target-i386/kvm.c b/target-i386/kvm.c
index 06474d6..e2f7e2e 100644
--- a/target-i386/kvm.c
+++ b/target-i386/kvm.c
@@ -817,7 +817,15 @@
     kvm_msr_entry_set(&msrs[n++], MSR_LSTAR, env->lstar);
 #endif
     if (level == KVM_PUT_FULL_STATE) {
-        kvm_msr_entry_set(&msrs[n++], MSR_IA32_TSC, env->tsc);
+        /*
+         * KVM is yet unable to synchronize TSC values of multiple VCPUs on
+         * writeback. Until this is fixed, we only write the offset to SMP
+         * guests after migration, desynchronizing the VCPUs, but avoiding
+         * huge jump-backs that would occur without any writeback at all.
+         */
+        if (smp_cpus == 1 || env->tsc != 0) {
+            kvm_msr_entry_set(&msrs[n++], MSR_IA32_TSC, env->tsc);
+        }
         kvm_msr_entry_set(&msrs[n++], MSR_KVM_SYSTEM_TIME,
                           env->system_time_msr);
         kvm_msr_entry_set(&msrs[n++], MSR_KVM_WALL_CLOCK, env->wall_clock_msr);