[Xen-devel] [PATCH v5] libxl: fix migration of PV and PVH domUs with and without qemu

Olaf Hering posted 1 patch 10 weeks ago
Failed in applying to current master (apply log)
tools/libxl/libxl.h             |  7 +++++++
tools/libxl/libxl_create.c      | 17 ++++++++++++++---
tools/libxl/libxl_dom_suspend.c |  8 ++++++--
tools/libxl/libxl_types.idl     |  1 +
4 files changed, 28 insertions(+), 5 deletions(-)

[Xen-devel] [PATCH v5] libxl: fix migration of PV and PVH domUs with and without qemu

Posted by Olaf Hering 10 weeks ago
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() used to hardcode
b_info->device_model_version to QEMU_XEN if it does not know it any
better. As a result libxl__device_model_version_running() will return
incorrect values. 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 the assumption
that every domU has a QEMU_XEN, 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 a device_model has to be spawned. This
function can not be used as is, just to fill device_model_version,
because store_libxl_entry() was already called earlier.

Introduce LIBXL_DEVICE_MODEL_VERSION_NONE for PV and PVH that have no
need for a device_model to make the state explicit. Indicate this new
state via LIBXL_HAVE macro in libxl.h.

v05:
- move initialization of device_model_version to extra commit
- return error from libxl__need_xenpv_qemu
- add LIBXL_HAVE_DEVICE_MODEL_VERSION_NONE
v04:
- make sure device_model_stubdomain is initialized
v03:
- rearrange code to make sure device_model_version is initialized before
  store_libxl_entry() is called
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@aepfle.de>
Cc: Roger Pau Monné <roger.pau@citrix.com>
Cc: Anthony PERARD <anthony.perard@citrix.com>
---
 tools/libxl/libxl.h             |  7 +++++++
 tools/libxl/libxl_create.c      | 17 ++++++++++++++---
 tools/libxl/libxl_dom_suspend.c |  8 ++++++--
 tools/libxl/libxl_types.idl     |  1 +
 4 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index 482499a6c0..e0f6916b66 100644
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -1182,6 +1182,13 @@ void libxl_mac_copy(libxl_ctx *ctx, libxl_mac *dst, const libxl_mac *src);
  */
 #define LIBXL_HAVE_PVCALLS 1
 
+/*
+ * LIBXL_HAVE_DEVICE_MODEL_VERSION_NONE
+ *
+ * If this is defined, libxl will only run a device-model if required.
+ */
+#define LIBXL_HAVE_DEVICE_MODEL_VERSION_NONE 1
+
 typedef char **libxl_string_list;
 void libxl_string_list_dispose(libxl_string_list *sl);
 int libxl_string_list_length(const libxl_string_list *sl);
diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index 3f0431cc84..64336b0d29 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -47,9 +47,20 @@ int libxl__domain_set_device_model(libxl__gc *gc, libxl_domain_config *d_config)
         }
         break;
     default:
-        b_info->device_model_version =
-            LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN_TRADITIONAL;
-        break;
+        ret = libxl__need_xenpv_qemu(gc, d_config);
+        switch (ret) {
+        case 1:
+            d_config->b_info.device_model_version =
+                LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN;
+            break;
+        case 0:
+            d_config->b_info.device_model_version =
+                LIBXL_DEVICE_MODEL_VERSION_NONE;
+            break;
+        default:
+            LOGE(ERROR, "Unable to determine QEMU requisite");
+            return ret;
+        }
     }
 
     if (b_info->device_model_version == LIBXL_DEVICE_MODEL_VERSION_QEMU_XEN) {
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_types.idl b/tools/libxl/libxl_types.idl
index cb4702fd7a..75bde095bc 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"),
     ])
 
 libxl_console_type = Enumeration("console_type", [

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Re: [Xen-devel] [PATCH v5] libxl: fix migration of PV and PVH domUs with and without qemu

Posted by Roger Pau Monné 10 weeks ago
On Tue, May 14, 2019 at 10:05:58AM +0200, Olaf Hering wrote:
> 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() used to hardcode
> b_info->device_model_version to QEMU_XEN if it does not know it any
> better. As a result libxl__device_model_version_running() will return
> incorrect values. 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 the assumption
> that every domU has a QEMU_XEN, 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 a device_model has to be spawned. This
> function can not be used as is, just to fill device_model_version,
> because store_libxl_entry() was already called earlier.
> 
> Introduce LIBXL_DEVICE_MODEL_VERSION_NONE for PV and PVH that have no
> need for a device_model to make the state explicit. Indicate this new
> state via LIBXL_HAVE macro in libxl.h.
> 
> v05:
> - move initialization of device_model_version to extra commit
> - return error from libxl__need_xenpv_qemu
> - add LIBXL_HAVE_DEVICE_MODEL_VERSION_NONE
> v04:
> - make sure device_model_stubdomain is initialized
> v03:
> - rearrange code to make sure device_model_version is initialized before
>   store_libxl_entry() is called
> 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@aepfle.de>

Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

Thanks, Roger.

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Re: [Xen-devel] [PATCH v5] libxl: fix migration of PV and PVH domUs with and without qemu

Posted by Olaf Hering 10 weeks ago
Am Tue, 14 May 2019 10:05:58 +0200
schrieb Olaf Hering <olaf@aepfle.de>:

> @@ -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);

I think this could be done like that instead, so that libxl__device_model_version_running
is called just once:

--- a/tools/libxl/libxl_dom_suspend.c
+++ b/tools/libxl/libxl_dom_suspend.c
@@ -444,6 +444,8 @@ int libxl__domain_resume_device_model(libxl__gc *gc, uint32_t domid)
         if (libxl__qmp_resume(gc, domid))
             return ERROR_FAIL;
         break;
+    case LIBXL_DEVICE_MODEL_VERSION_NONE:
+        break;
     default:
         return ERROR_INVAL;
     }
@@ -461,14 +463,10 @@ int libxl__domain_resume(libxl__gc *gc, uint32_t domid, int suspend_cancel)
         goto out;
     }
 
-    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);
-            goto out;
-        }
+    rc = libxl__domain_resume_device_model(gc, domid);
+    if (rc) {
+        LOGD(ERROR, domid, "failed to resume device model:%d", rc);
+        goto out;
     }
 
     if (xc_domain_resume(CTX->xch, domid, suspend_cancel)) {


While it is easy for the resume path, doing the same in the suspend path
needs more changes. libxl__domain_suspend_device_model would need to receive
the callback and set it if a device model is active.

Should this be done on top of this change?

Olaf
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Re: [Xen-devel] [PATCH v5] libxl: fix migration of PV and PVH domUs with and without qemu

Posted by Wei Liu 10 weeks ago
On Tue, May 14, 2019 at 10:14:52AM +0200, Olaf Hering wrote:
> Am Tue, 14 May 2019 10:05:58 +0200
> schrieb Olaf Hering <olaf@aepfle.de>:
> 
> > @@ -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);
> 
> I think this could be done like that instead, so that libxl__device_model_version_running
> is called just once:
> 
> --- a/tools/libxl/libxl_dom_suspend.c
> +++ b/tools/libxl/libxl_dom_suspend.c
> @@ -444,6 +444,8 @@ int libxl__domain_resume_device_model(libxl__gc *gc, uint32_t domid)
>          if (libxl__qmp_resume(gc, domid))
>              return ERROR_FAIL;
>          break;
> +    case LIBXL_DEVICE_MODEL_VERSION_NONE:
> +        break;
>      default:
>          return ERROR_INVAL;
>      }
> @@ -461,14 +463,10 @@ int libxl__domain_resume(libxl__gc *gc, uint32_t domid, int suspend_cancel)
>          goto out;
>      }
>  
> -    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);
> -            goto out;
> -        }
> +    rc = libxl__domain_resume_device_model(gc, domid);
> +    if (rc) {
> +        LOGD(ERROR, domid, "failed to resume device model:%d", rc);
> +        goto out;
>      }
>  
>      if (xc_domain_resume(CTX->xch, domid, suspend_cancel)) {
> 

Yeah, from the look of it this is definitely better.

> 
> While it is easy for the resume path, doing the same in the suspend path
> needs more changes. libxl__domain_suspend_device_model would need to receive
> the callback and set it if a device model is active.

What do you mean here? Can't you handle the NONE case just like you do
in the resume function?

Wei.

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Re: [Xen-devel] [PATCH v5] libxl: fix migration of PV and PVH domUs with and without qemu

Posted by Olaf Hering 10 weeks ago
Am Tue, 14 May 2019 15:38:55 +0100
schrieb Wei Liu <wei.liu2@citrix.com>:

> > While it is easy for the resume path, doing the same in the suspend path
> > needs more changes. libxl__domain_suspend_device_model would need to receive
> > the callback and set it if a device model is active.  
> 
> What do you mean here? Can't you handle the NONE case just like you do
> in the resume function?

It means calling libxl__domain_suspend_device_model unconditionally, and
let that function decide what to do. Maybe there is no downside to set the
callback unconditionally, I will check that.

Olaf
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Re: [Xen-devel] [PATCH v5] libxl: fix migration of PV and PVH domUs with and without qemu

Posted by Wei Liu 10 weeks ago
On Tue, May 14, 2019 at 04:44:19PM +0200, Olaf Hering wrote:
> Am Tue, 14 May 2019 15:38:55 +0100
> schrieb Wei Liu <wei.liu2@citrix.com>:
> 
> > > While it is easy for the resume path, doing the same in the suspend path
> > > needs more changes. libxl__domain_suspend_device_model would need to receive
> > > the callback and set it if a device model is active.  
> > 
> > What do you mean here? Can't you handle the NONE case just like you do
> > in the resume function?
> 
> It means calling libxl__domain_suspend_device_model unconditionally, and
> let that function decide what to do. Maybe there is no downside to set the
> callback unconditionally, I will check that.

Sure. In the meantime I will apply this patch at some point to fix the
bug first.

Wei.

> 
> Olaf



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