From c6af8b2be6ba25125efd9ed96e2464da96f23315 Mon Sep 17 00:00:00 2001
Message-ID: <c6af8b2be6ba25125efd9ed96e2464da96f23315.1710860841.git.jdenemar@redhat.com>
From: Jiri Denemark <jdenemar@redhat.com>
Date: Mon, 11 Mar 2024 17:04:48 +0100
Subject: [PATCH] qemu: domain: Drop added features from migratable CPU

Features marked with added='yes' in CPU model definitions have to be
removed before migration, otherwise older libvirt would complain about
unknown CPU features. We only do this for features that were enabled for
a given CPU model even with older libvirt, which just ignored the
features. And only for features we added ourselves when updating CPU
definition during domain startup, that is we do not remove features
which were explicitly mentioned by a user.

That said, this is not the safest thing we could do, but it's
effectively the same thing we did before the affected features were
added: we ignored them completely on both sides of migration.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Tim Wiederhake <twiederh@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>
(cherry picked from commit 14d3517410021d59cb53fb4c841a5d9922e814d1)
https://issues.redhat.com/browse/RHEL-25995

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
---
 src/qemu/qemu_domain.c           | 50 ++++++++++++++++++++++++++++++--
 src/qemu/qemu_domain.h           |  3 +-
 src/qemu/qemu_migration_cookie.c |  5 +++-
 3 files changed, 54 insertions(+), 4 deletions(-)

diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index 8e7665b198..1daa53dd1b 100644
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -66,6 +66,7 @@
 #include "backup_conf.h"
 #include "virutil.h"
 #include "virsecureerase.h"
+#include "cpu/cpu_x86.h"
 
 #include <sys/time.h>
 #include <fcntl.h>
@@ -6587,10 +6588,36 @@ qemuDomainDefCopy(virQEMUDriver *driver,
 }
 
 
+typedef struct {
+    const char * const *added;
+    GStrv keep;
+} qemuDomainDropAddedCPUFeaturesData;
+
+
+static bool
+qemuDomainDropAddedCPUFeatures(const char *name,
+                               virCPUFeaturePolicy policy G_GNUC_UNUSED,
+                               void *opaque)
+{
+    qemuDomainDropAddedCPUFeaturesData *data = opaque;
+
+    if (!g_strv_contains(data->added, name))
+        return true;
+
+    if (data->keep && g_strv_contains((const char **) data->keep, name))
+        return true;
+
+    return false;
+}
+
+
 int
 qemuDomainMakeCPUMigratable(virArch arch,
-                            virCPUDef *cpu)
+                            virCPUDef *cpu,
+                            virCPUDef *origCPU)
 {
+    qemuDomainDropAddedCPUFeaturesData data = { 0 };
+
     if (cpu->mode != VIR_CPU_MODE_CUSTOM ||
         !cpu->model ||
         !ARCH_IS_X86(arch))
@@ -6608,6 +6635,25 @@ qemuDomainMakeCPUMigratable(virArch arch,
             return -1;
     }
 
+    if (virCPUx86GetAddedFeatures(cpu->model, &data.added) < 0)
+        return -1;
+
+    /* Drop features marked as added in a cpu model, but only
+     * when they are not mentioned in origCPU, i.e., when they were not
+     * explicitly mentioned by the user.
+     */
+    if (data.added) {
+        g_auto(GStrv) keep = NULL;
+
+        if (origCPU) {
+            keep = virCPUDefListExplicitFeatures(origCPU);
+            data.keep = keep;
+        }
+
+        if (virCPUDefFilterFeatures(cpu, qemuDomainDropAddedCPUFeatures, &data) < 0)
+            return -1;
+    }
+
     return 0;
 }
 
@@ -6787,7 +6833,7 @@ qemuDomainDefFormatBufInternal(virQEMUDriver *driver,
         }
 
         if (def->cpu &&
-            qemuDomainMakeCPUMigratable(def->os.arch, def->cpu) < 0)
+            qemuDomainMakeCPUMigratable(def->os.arch, def->cpu, origCPU) < 0)
             return -1;
 
         /* Old libvirt doesn't understand <audio> elements so
diff --git a/src/qemu/qemu_domain.h b/src/qemu/qemu_domain.h
index a7a8bcc460..d98f1c0a99 100644
--- a/src/qemu/qemu_domain.h
+++ b/src/qemu/qemu_domain.h
@@ -1046,7 +1046,8 @@ qemuDomainSupportsCheckpointsBlockjobs(virDomainObj *vm)
 
 int
 qemuDomainMakeCPUMigratable(virArch arch,
-                            virCPUDef *cpu);
+                            virCPUDef *cpu,
+                            virCPUDef *origCPU);
 
 int
 qemuDomainInitializePflashStorageSource(virDomainObj *vm,
diff --git a/src/qemu/qemu_migration_cookie.c b/src/qemu/qemu_migration_cookie.c
index c53d42a018..90cc079c1a 100644
--- a/src/qemu/qemu_migration_cookie.c
+++ b/src/qemu/qemu_migration_cookie.c
@@ -540,12 +540,15 @@ static int
 qemuMigrationCookieAddCPU(qemuMigrationCookie *mig,
                           virDomainObj *vm)
 {
+    qemuDomainObjPrivate *priv = vm->privateData;
+
     if (mig->cpu)
         return 0;
 
     mig->cpu = virCPUDefCopy(vm->def->cpu);
 
-    if (qemuDomainMakeCPUMigratable(vm->def->os.arch, mig->cpu) < 0)
+    if (qemuDomainMakeCPUMigratable(vm->def->os.arch, mig->cpu,
+                                    priv->origCPU) < 0)
         return -1;
 
     mig->flags |= QEMU_MIGRATION_COOKIE_CPU;
-- 
2.44.0