Commit 561dbb41b1d7 "i386: Make migration fail when Hyper-V reenlightenment
was enabled but 'user_tsc_khz' is unset" forbade migrations with when guest
has opted for reenlightenment notifications but 'tsc-frequency' wasn't set
explicitly on the command line. This works but the migration fails late and
this may come as an unpleasant surprise. To make things more explicit,
add a migration blocker when 'hv-reenlightenment' was enabled but
'tsc-frequency' is unset. Make the change affect 6.0+ machine types only to
preserve previously-valid configurations.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
Changes since v2:
- Use migrate_add_blocker() [Eduardo]

Note: In case this patch gets queued for 6.1 an adjustment is needed:

   { TYPE_X86_CPU, "x-hv-reenlightenment-requires-tscfreq", "off"}

needs to go to not-yet-existing 'pc_compat_6_0'.
---
 docs/hyperv.txt   |  1 +
 hw/i386/pc.c      |  1 +
 target/i386/cpu.c | 34 ++++++++++++++++++++++++++++++++--
 target/i386/cpu.h |  1 +
 4 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/docs/hyperv.txt b/docs/hyperv.txt
index e53c581f4586..d20b5c58c847 100644
--- a/docs/hyperv.txt
+++ b/docs/hyperv.txt
@@ -165,6 +165,7 @@ emulate TSC accesses after migration so 'tsc-frequency=' CPU option also has to
 be specified to make migration succeed. The destination host has to either have
 the same TSC frequency or support TSC scaling CPU feature.
 
+Requires: tsc-frequency (for migration)
 Recommended: hv-frequencies
 
 3.16. hv-evmcs
diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 8a84b25a031e..47b79e949ad7 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -98,6 +98,7 @@
 
 GlobalProperty pc_compat_5_2[] = {
     { "ICH9-LPC", "x-smi-cpu-hotunplug", "off" },
+    { TYPE_X86_CPU, "x-hv-reenlightenment-requires-tscfreq", "off"},
 };
 const size_t pc_compat_5_2_len = G_N_ELEMENTS(pc_compat_5_2);
 
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 6b3e9467f177..f74239acd12b 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -56,6 +56,7 @@
 #include "sysemu/tcg.h"
 #include "hw/qdev-properties.h"
 #include "hw/i386/topology.h"
+#include "migration/blocker.h"
 #ifndef CONFIG_USER_ONLY
 #include "exec/address-spaces.h"
 #include "hw/i386/apic_internal.h"
@@ -6647,10 +6648,33 @@ static void x86_cpu_filter_features(X86CPU *cpu, bool verbose)
     }
 }
 
-static void x86_cpu_hyperv_realize(X86CPU *cpu)
+static Error *hv_reenlightenment_mig_blocker;
+
+static void x86_cpu_hyperv_realize(X86CPU *cpu, Error **errp)
 {
+    CPUX86State *env = &cpu->env;
+    Error *local_err = NULL;
     size_t len;
 
+    /*
+     * Reenlightenment requires explicit 'tsc-frequency' setting for successful
+     * migration (see hyperv_reenlightenment_post_load()). As 'hv-passthrough'
+     * mode is not migratable, we can loosen the restriction.
+     */
+    if (hyperv_feat_enabled(cpu, HYPERV_FEAT_REENLIGHTENMENT) &&
+        !cpu->hyperv_passthrough && !env->user_tsc_khz &&
+        cpu->hyperv_reenlightenment_requires_tscfreq) {
+
+        error_setg(&hv_reenlightenment_mig_blocker,
+                   "'hv-reenlightenment' requires 'tsc-frequency' to be set");
+
+        migrate_add_blocker(hv_reenlightenment_mig_blocker, &local_err);
+        if (local_err != NULL) {
+            error_propagate(errp, local_err);
+            return;
+        }
+    }
+
     /* Hyper-V vendor id */
     if (!cpu->hyperv_vendor) {
         memcpy(cpu->hyperv_vendor_id, "Microsoft Hv", 12);
@@ -6846,7 +6870,11 @@ static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
     }
 
     /* Process Hyper-V enlightenments */
-    x86_cpu_hyperv_realize(cpu);
+    x86_cpu_hyperv_realize(cpu, &local_err);
+    if (local_err != NULL) {
+        error_propagate(errp, local_err);
+        return;
+    }
 
     cpu_exec_realizefn(cs, &local_err);
     if (local_err != NULL) {
@@ -7374,6 +7402,8 @@ static Property x86_cpu_properties[] = {
     DEFINE_PROP_INT32("x-hv-max-vps", X86CPU, hv_max_vps, -1),
     DEFINE_PROP_BOOL("x-hv-synic-kvm-only", X86CPU, hyperv_synic_kvm_only,
                      false),
+    DEFINE_PROP_BOOL("x-hv-reenlightenment-requires-tscfreq", X86CPU,
+                     hyperv_reenlightenment_requires_tscfreq, true),
     DEFINE_PROP_BOOL("x-intel-pt-auto-level", X86CPU, intel_pt_auto_level,
                      true),
     DEFINE_PROP_END_OF_LIST()
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 570f916878f9..0196a300f018 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -1677,6 +1677,7 @@ struct X86CPU {
     uint32_t hyperv_spinlock_attempts;
     char *hyperv_vendor;
     bool hyperv_synic_kvm_only;
+    bool hyperv_reenlightenment_requires_tscfreq;
     uint64_t hyperv_features;
     bool hyperv_passthrough;
     OnOffAuto hyperv_no_nonarch_cs;
-- 
2.30.2