[Qemu-devel] [patch 2/2] target-i386: block migration and savevm if invariant tsc is exposed

[Marcelo Tosatti]

Invariant TSC documentation mentions that "invariant TSC will run at a
constant rate in all ACPI P-, C-. and T-states".

This is not the case if migration to a host with different TSC frequency 
is allowed, or if savevm is performed. So block migration/savevm.

Also do not expose invariant tsc flag by default.

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

Index: qemu-invariant-tsc/target-i386/kvm.c
===================================================================
--- qemu-invariant-tsc.orig/target-i386/kvm.c
+++ qemu-invariant-tsc/target-i386/kvm.c
@@ -33,6 +33,8 @@
 #include "exec/ioport.h"
 #include <asm/hyperv.h>
 #include "hw/pci/pci.h"
+#include "migration/migration.h"
+#include "qapi/qmp/qerror.h"
 
 //#define DEBUG_KVM
 
@@ -447,6 +449,8 @@ static bool hyperv_enabled(X86CPU *cpu)
             cpu->hyperv_relaxed_timing);
 }
 
+Error *invtsc_mig_blocker;
+
 #define KVM_MAX_CPUID_ENTRIES  100
 
 int kvm_arch_init_vcpu(CPUState *cs)
@@ -702,6 +706,16 @@ int kvm_arch_init_vcpu(CPUState *cs)
                                   !!(c->ecx & CPUID_EXT_SMX);
     }
 
+    c = cpuid_find_entry(&cpuid_data.cpuid, 0x80000007, 0);
+    if (c && (c->edx & 1<<8)) {
+        /* for migration */
+        invtsc_mig_blocker = NULL;
+        error_set(&invtsc_mig_blocker, QERR_MIGRATION_NOT_SUPPORTED, "cpu");
+        migrate_add_blocker(invtsc_mig_blocker);
+        /* for savevm */
+        vmstate_x86_cpu.unmigratable = 1;
+    }
+
     cpuid_data.cpuid.padding = 0;
     r = kvm_vcpu_ioctl(cs, KVM_SET_CPUID2, &cpuid_data);
     if (r) {
Index: qemu-invariant-tsc/target-i386/cpu-qom.h
===================================================================
--- qemu-invariant-tsc.orig/target-i386/cpu-qom.h
+++ qemu-invariant-tsc/target-i386/cpu-qom.h
@@ -116,7 +116,7 @@ static inline X86CPU *x86_env_get_cpu(CP
 #define ENV_OFFSET offsetof(X86CPU, env)
 
 #ifndef CONFIG_USER_ONLY
-extern const struct VMStateDescription vmstate_x86_cpu;
+extern struct VMStateDescription vmstate_x86_cpu;
 #endif
 
 /**
Index: qemu-invariant-tsc/target-i386/machine.c
===================================================================
--- qemu-invariant-tsc.orig/target-i386/machine.c
+++ qemu-invariant-tsc/target-i386/machine.c
@@ -613,7 +613,7 @@ static const VMStateDescription vmstate_
     }
 };
 
-const VMStateDescription vmstate_x86_cpu = {
+VMStateDescription vmstate_x86_cpu = {
     .name = "cpu",
     .version_id = 12,
     .minimum_version_id = 3,
Index: qemu-invariant-tsc/target-i386/cpu.c
===================================================================
--- qemu-invariant-tsc.orig/target-i386/cpu.c
+++ qemu-invariant-tsc/target-i386/cpu.c
@@ -1230,6 +1230,8 @@ static void host_x86_cpu_initfn(Object *
 
     for (w = 0; w < FEATURE_WORDS; w++) {
         FeatureWordInfo *wi = &feature_word_info[w];
+        if (w == FEAT_8000_0007_EDX)
+            continue;
         env->features[w] =
             kvm_arch_get_supported_cpuid(s, wi->cpuid_eax, wi->cpuid_ecx,
                                          wi->cpuid_reg);