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[Xen-devel] [PATCH v2] libxl: fix migration of PV and PVH domUs with and without qemu



If a domU has a qemu-xen instance attached, it is required to call qemus
"xen-save-devices-state" method. Without it, the receiving side of a PV or
PVH migration may be unable to lock the image:

xen be: qdisk-51712: xen be: qdisk-51712: error: Failed to get "write" lock
error: Failed to get "write" lock
xen be: qdisk-51712: xen be: qdisk-51712: initialise() failed
initialise() failed

To fix this bug, libxl__domain_suspend_device_model() and
libxl__domain_resume_device_model() have to be called not only for HVM,
but also if the active device_model is QEMU_XEN.

Unfortunately, libxl__domain_build_info_setdefault() hardcodes
b_info->device_model_version to QEMU_XEN if it does not know it any
better. This breaks domUs without a device_model. libxl__qmp_stop() would
wait 10 seconds in qmp_open() for a qemu that will never appear.  During
this long timeframe the domU remains in state paused on the sending side.
As a result network connections may be dropped. Once this bug is fixed as
well, by just removing that assumption, there is no code to actually
initialise b_info->device_model_version.

There is a helper function libxl__need_xenpv_qemu(), which is used in
various places to decide if any device_model has to be spawned. This
function can not be used as is, just to fill b_info->device_model_version,
because store_libxl_entry() was already called earlier. Update this
function to receive a domid to work with, instead of reading xenstore.

Rearrange the code and initialize b_info->device_model_version in
libxl__domain_build_info_setdefault() per DOMAIN_TYPE.

Update initiate_domain_create() to set b_info->device_model_version if it
was not set earlier, using the updated libxl__need_xenpv_qemu().

Introduce LIBXL_DEVICE_MODEL_VERSION_NONE_REQUIRED for PV and PVH that
have no need for a device_model.

Update existing users of libxl__need_xenpv_qemu() to use
b_info->device_model_version for their check if a device_model is needed.

v02:
- update wording in a comment
- remove stale goto in domcreate_launch_dm
- initialize ret in libxl__need_xenpv_qemu

Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Cc: Anthony PERARD <anthony.perard@xxxxxxxxxx>
---
 tools/libxl/libxl_create.c      | 39 +++++++++++++++++++++++++++++++--------
 tools/libxl/libxl_dm.c          | 40 +++++++++++++++++++++++-----------------
 tools/libxl/libxl_dom_suspend.c |  8 ++++++--
 tools/libxl/libxl_internal.h    |  3 ++-
 tools/libxl/libxl_types.idl     |  1 +
 5 files changed, 63 insertions(+), 28 deletions(-)

diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index 89fe80fc9c..150ab02354 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -87,16 +87,20 @@ int libxl__domain_build_info_setdefault(libxl__gc *gc,
         b_info->device_model_ssidref = SECINITSID_DOMDM;
 
     if (!b_info->device_model_version) {
-        if (b_info->type == LIBXL_DOMAIN_TYPE_HVM) {
+        switch (b_info->type) {
+        case LIBXL_DOMAIN_TYPE_HVM:
             if (libxl_defbool_val(b_info->device_model_stubdomain)) {
                 b_info->device_model_version =
                     LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN_TRADITIONAL;
             } else {
                 b_info->device_model_version = libxl__default_device_model(gc);
             }
-        } else {
-            b_info->device_model_version =
-                LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN;
+            break;
+        case LIBXL_DOMAIN_TYPE_PV:
+        case LIBXL_DOMAIN_TYPE_PVH:
+        default:
+            /* may be set later */
+            break;
         }
         if (b_info->device_model_version
                 == LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN) {
@@ -978,6 +982,17 @@ static void initiate_domain_create(libxl__egc *egc,
         goto error_out;
     }
 
+    if (d_config->b_info.device_model_version
+        == LIBXL_DEVICE_MODEL_VERSION_UNKNOWN) {
+        ret = libxl__need_xenpv_qemu(gc, d_config, domid);
+        if (ret)
+            d_config->b_info.device_model_version =
+                LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN;
+        else
+            d_config->b_info.device_model_version =
+                LIBXL_DEVICE_MODEL_VERSION_NONE_REQUIRED;
+    }
+
     dcs->guest_domid = domid;
     dcs->sdss.dm.guest_domid = 0; /* means we haven't spawned */
 
@@ -1312,6 +1327,7 @@ static void domcreate_launch_dm(libxl__egc *egc, 
libxl__multidev *multidev,
     libxl__domain_create_state *dcs = CONTAINER_OF(multidev, *dcs, multidev);
     STATE_AO_GC(dcs->ao);
     int i;
+    bool need_qemu;
 
     /* convenience aliases */
     const uint32_t domid = dcs->guest_domid;
@@ -1464,10 +1480,17 @@ static void domcreate_launch_dm(libxl__egc *egc, 
libxl__multidev *multidev,
         libxl__device_console_add(gc, domid, &console, state, &device);
         libxl__device_console_dispose(&console);
 
-        ret = libxl__need_xenpv_qemu(gc, d_config);
-        if (ret < 0)
-            goto error_out;
-        if (ret) {
+        switch (d_config->b_info.device_model_version) {
+            case LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN_TRADITIONAL:
+            case LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN:
+                need_qemu = true;
+                break;
+            default:
+                need_qemu = false;
+                break;
+        }
+
+        if (need_qemu) {
             dcs->sdss.dm.guest_domid = domid;
             libxl__spawn_local_dm(egc, &dcs->sdss.dm);
             return;
diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
index 2f19786bdd..bab04ab196 100644
--- a/tools/libxl/libxl_dm.c
+++ b/tools/libxl/libxl_dm.c
@@ -2268,7 +2268,7 @@ static void spawn_stub_launch_dm(libxl__egc *egc,
     libxl__domain_build_state *const d_state = sdss->dm.build_state;
     libxl__domain_build_state *const stubdom_state = &sdss->dm_state;
     uint32_t dm_domid = sdss->pvqemu.guest_domid;
-    int need_qemu;
+    bool need_qemu;
 
     if (ret) {
         LOGD(ERROR, guest_domid, "error connecting disk devices");
@@ -2337,7 +2337,15 @@ static void spawn_stub_launch_dm(libxl__egc *egc,
         }
     }
 
-    need_qemu = libxl__need_xenpv_qemu(gc, dm_config);
+    switch (dm_config->b_info.device_model_version) {
+        case LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN_TRADITIONAL:
+        case LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN:
+            need_qemu = true;
+            break;
+        default:
+            need_qemu = false;
+            break;
+    }
 
     for (i = 0; i < num_console; i++) {
         libxl__device device;
@@ -3175,18 +3183,11 @@ static void kill_device_model_uid_cb(libxl__egc *egc,
 }
 
 /* Return 0 if no dm needed, 1 if needed and <0 if error. */
-int libxl__need_xenpv_qemu(libxl__gc *gc, libxl_domain_config *d_config)
+int libxl__need_xenpv_qemu(libxl__gc *gc, libxl_domain_config *d_config, 
uint32_t domid)
 {
-    int idx, i, ret, num;
-    uint32_t domid;
+    int idx, i, ret = 0, num;
     const struct libxl_device_type *dt;
 
-    ret = libxl__get_domid(gc, &domid);
-    if (ret) {
-        LOG(ERROR, "unable to get domain id");
-        goto out;
-    }
-
     if (d_config->num_vfbs > 0 || d_config->num_p9s > 0) {
         ret = 1;
         goto out;
@@ -3238,21 +3239,26 @@ int libxl__dm_check_start(libxl__gc *gc, 
libxl_domain_config *d_config,
                           uint32_t domid)
 {
     int rc;
+    bool need_qemu;
 
     if (libxl__dm_active(gc, domid))
         return 0;
 
-    rc = libxl__need_xenpv_qemu(gc, d_config);
-    if (rc < 0)
-        goto out;
-
-    if (!rc)
+    switch (d_config->b_info.device_model_version) {
+        case LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN_TRADITIONAL:
+        case LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN:
+            need_qemu = true;
+            break;
+        default:
+            need_qemu = false;
+            break;
+    }
+    if (need_qemu == false)
         return 0;
 
     LOGD(ERROR, domid, "device model required but not running");
     rc = ERROR_FAIL;
 
-out:
     return rc;
 }
 
diff --git a/tools/libxl/libxl_dom_suspend.c b/tools/libxl/libxl_dom_suspend.c
index d1af3a6573..c492fe5dd1 100644
--- a/tools/libxl/libxl_dom_suspend.c
+++ b/tools/libxl/libxl_dom_suspend.c
@@ -379,7 +379,9 @@ static void 
domain_suspend_common_guest_suspended(libxl__egc *egc,
     libxl__ev_xswatch_deregister(gc, &dsps->guest_watch);
     libxl__ev_time_deregister(gc, &dsps->guest_timeout);
 
-    if (dsps->type == LIBXL_DOMAIN_TYPE_HVM) {
+    if (dsps->type == LIBXL_DOMAIN_TYPE_HVM ||
+        libxl__device_model_version_running(gc, dsps->domid) ==
+        LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN) {
         dsps->callback_device_model_done = domain_suspend_common_done;
         libxl__domain_suspend_device_model(egc, dsps); /* must be last */
         return;
@@ -459,7 +461,9 @@ int libxl__domain_resume(libxl__gc *gc, uint32_t domid, int 
suspend_cancel)
         goto out;
     }
 
-    if (type == LIBXL_DOMAIN_TYPE_HVM) {
+    if (type == LIBXL_DOMAIN_TYPE_HVM ||
+        libxl__device_model_version_running(gc, domid) ==
+        LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN) {
         rc = libxl__domain_resume_device_model(gc, domid);
         if (rc) {
             LOGD(ERROR, domid, "failed to resume device model:%d", rc);
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 44e0221284..9eb4211d85 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -1817,7 +1817,8 @@ _hidden int libxl__domain_build(libxl__gc *gc,
 _hidden const char *libxl__domain_device_model(libxl__gc *gc,
                                         const libxl_domain_build_info *info);
 _hidden int libxl__need_xenpv_qemu(libxl__gc *gc,
-                                   libxl_domain_config *d_config);
+                                   libxl_domain_config *d_config,
+                                   uint32_t domid);
 _hidden bool libxl__query_qemu_backend(libxl__gc *gc,
                                        uint32_t domid,
                                        uint32_t backend_id,
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index cb4702fd7a..7d75bd3850 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -106,6 +106,7 @@ libxl_device_model_version = 
Enumeration("device_model_version", [
     (0, "UNKNOWN"),
     (1, "QEMU_XEN_TRADITIONAL"), # Historical qemu-xen device model (qemu-dm)
     (2, "QEMU_XEN"),             # Upstream based qemu-xen device model
+    (3, "NONE_REQUIRED"),
     ])
 
 libxl_console_type = Enumeration("console_type", [

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