From 579a6f80e0ea312e9c113bd79be8bef36eabb090 Mon Sep 17 00:00:00 2001
From: Bruce Rogers <brogers@suse.com>
Date: Wed, 21 Feb 2018 14:00:52 -0700
Subject: [PATCH] migration: warn about inconsistent spec_ctrl state

As an attempt to help the user do the right thing, warn if we
detect spec_ctrl data in the migration stream, but where the
cpu defined doesn't have the feature. This would indicate the
migration is from the quick and dirty qemu produced in January
2018 to handle Spectre v2. That qemu version exposed the IBRS
cpu feature to all vcpu types, which helped in the short term
but wasn't a well designed approach.
Warn the user that the now migrated guest needs to be restarted
as soon as possible, using the spec_ctrl cpu feature flag or a
*-IBRS vcpu model specified as appropriate.

Signed-off-by: Bruce Rogers <brogers@suse.com>
---
 cpus.c                | 12 ++++++++++++
 include/qemu/thread.h |  1 +
 migration/migration.c |  8 ++++++++
 3 files changed, 21 insertions(+)

diff --git a/cpus.c b/cpus.c
index b5844b7103..2717f2e105 100644
--- a/cpus.c
+++ b/cpus.c
@@ -2367,6 +2367,18 @@ exit:
     fclose(f);
 }
 
+bool spec_ctrl_is_inconsistent(void)
+{
+#if defined(TARGET_I386)
+    X86CPU *x86_cpu = X86_CPU(current_cpu);
+    CPUX86State *env = x86_cpu != NULL ? &x86_cpu->env : NULL;
+    if (env && !(env->features[FEAT_7_0_EDX] & CPUID_7_0_EDX_SPEC_CTRL) &&
+	    env->spec_ctrl)
+        return true;
+#endif
+    return false;
+}
+
 void qmp_inject_nmi(Error **errp)
 {
     nmi_monitor_handle(monitor_get_cpu_index(), errp);
diff --git a/include/qemu/thread.h b/include/qemu/thread.h
index ef7bd16123..c4ecb386fe 100644
--- a/include/qemu/thread.h
+++ b/include/qemu/thread.h
@@ -240,4 +240,5 @@ void qemu_lockcnt_inc_and_unlock(QemuLockCnt *lockcnt);
  */
 unsigned qemu_lockcnt_count(QemuLockCnt *lockcnt);
 
+bool spec_ctrl_is_inconsistent(void);
 #endif
diff --git a/migration/migration.c b/migration/migration.c
index b7d9854bda..31b4d8bd28 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -2575,6 +2575,14 @@ static void migration_completion(MigrationState *s)
         migrate_set_state(&s->state, current_active_state,
                           MIGRATION_STATUS_COMPLETED);
     }
+    if (spec_ctrl_is_inconsistent()) {
+        fprintf(stderr, "WARNING! Migration from qemu with rudimentary "
+                        "Spectre v2 support to newer qemu\ndetected! To "
+                        "maintain proper protection, restart the guest as "
+                        "soon as possible\nusing the spec_ctrl cpu feature "
+                        "flag or a *-IBRS vcpu model specified\nas appropriate."
+                        "\n");
+    }
 
     return;