From 555715ac88c361e4c9b262235010c265729738bf 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 d1e7e28993..1bfdb155dc 100644
--- a/cpus.c
+++ b/cpus.c
@@ -2039,6 +2039,18 @@ 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 9910f49b3a..c5803bfacc 100644
--- a/include/qemu/thread.h
+++ b/include/qemu/thread.h
@@ -210,4 +210,5 @@ 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 d780601f0c..d39c43c6b7 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -2121,6 +2121,14 @@ static void migration_completion(MigrationState *s, int current_active_state,
         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;