Re: [Xen-devel] [PATCH for 4.6 v4 2/3] xl/libxl: disallow saving a guest with vNUMA configured

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Sep 11, 2015 at 03:24:21PM +0100, Ian Campbell wrote:
> On Fri, 2015-09-11 at 15:14 +0100, Wei Liu wrote:
> @@ -1636,6 +1638,20 @@ void libxl__domain_save(libxl__egc *egc,
> > libxl__domain_suspend_state *dss)
> >            | (debug ? XCFLAGS_DEBUG : 0)
> >            | (dss->hvm ? XCFLAGS_HVM : 0);
> >  
> > +    /* Disallow saving a guest with vNUMA configured because migration
> > +     * stream does not preserve node information.
> > +     *
> > +     * Do not differentiate "no vnuma configuration" from "empty vnuma
> > +     * configuration".
> > +     */
> > +    rc = xc_domain_getvnuma(CTX->xch, domid, &nr_vnodes, &nr_vmemranges,
> > +                            &nr_vcpus, NULL, NULL, NULL);
> 
> Sorry for not noticing this before but this is putting a non-libxl error
> code in a variable named rc, which is verboten in coding style.
> 

My bad. Should have noticed that earlier.

> Not least because I think it is now possible to get through this function
> successfully without changing it from the rc == -1 which might be assigned
> here (in the case where xs_suspend_evtchn_port returns < 0).
> 
> Ian.

Add a new variable called ret to store return value from xc function
call. Here is the patch.

---8<---
From c2e9567fa0c5a00405d3759321c9eefb8ec049fc Mon Sep 17 00:00:00 2001
From: Wei Liu <wei.liu2@xxxxxxxxxx>
Date: Wed, 9 Sep 2015 17:11:24 +0100
Subject: [PATCH] xl/libxl: disallow saving a guest with vNUMA configured

This is because the migration stream does not preserve node information.

Note this is not a regression for migration v2 vs legacy migration
because neither of them preserves node information.

Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
Cc: andrew.cooper3@xxxxxxxxxx

v4:
1. Don't differentiate "no vnuma" from "empty vnuma".
2. Use ret to store xc function call return value.

v3:
1. Update manpage, code comment and commit message.
2. *Don't* check if nomigrate is set.
---
 docs/man/xl.cfg.pod.5   |  2 ++
 tools/libxl/libxl_dom.c | 18 +++++++++++++++++-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
index c6345b8..157c855 100644
--- a/docs/man/xl.cfg.pod.5
+++ b/docs/man/xl.cfg.pod.5
@@ -263,6 +263,8 @@ virtual node.
 
 Note that virtual NUMA for PV guest is not yet supported, because
 there is an issue with cpuid handling that affects PV virtual NUMA.
+Further more, guest with virtual NUMA cannot be saved or migrated
+because migration stream does not preserve node information.
 
 Each B<VNODE_SPEC> is a list, which has a form of
 "[VNODE_CONFIG_OPTION,VNODE_CONFIG_OPTION, ... ]"  (without quotes).
diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
index c2518a3..905dc5a 100644
--- a/tools/libxl/libxl_dom.c
+++ b/tools/libxl/libxl_dom.c
@@ -24,6 +24,7 @@
 #include <xen/hvm/hvm_info_table.h>
 #include <xen/hvm/hvm_xs_strings.h>
 #include <xen/hvm/e820.h>
+#include <xen/errno.h>
 
 libxl_domain_type libxl__domain_type(libxl__gc *gc, uint32_t domid)
 {
@@ -1602,7 +1603,7 @@ void libxl__domain_save(libxl__egc *egc, 
libxl__domain_suspend_state *dss)
 {
     STATE_AO_GC(dss->ao);
     int port;
-    int rc;
+    int rc, ret;
 
     /* Convenience aliases */
     const uint32_t domid = dss->domid;
@@ -1612,6 +1613,7 @@ void libxl__domain_save(libxl__egc *egc, 
libxl__domain_suspend_state *dss)
     const libxl_domain_remus_info *const r_info = dss->remus;
     libxl__srm_save_autogen_callbacks *const callbacks =
         &dss->sws.shs.callbacks.save.a;
+    unsigned int nr_vnodes = 0, nr_vmemranges = 0, nr_vcpus = 0;
 
     dss->rc = 0;
     logdirty_init(&dss->logdirty);
@@ -1636,6 +1638,20 @@ void libxl__domain_save(libxl__egc *egc, 
libxl__domain_suspend_state *dss)
           | (debug ? XCFLAGS_DEBUG : 0)
           | (dss->hvm ? XCFLAGS_HVM : 0);
 
+    /* Disallow saving a guest with vNUMA configured because migration
+     * stream does not preserve node information.
+     *
+     * Do not differentiate "no vnuma configuration" from "empty vnuma
+     * configuration".
+     */
+    ret = xc_domain_getvnuma(CTX->xch, domid, &nr_vnodes, &nr_vmemranges,
+                             &nr_vcpus, NULL, NULL, NULL);
+    if (ret != -1 || errno != XEN_EOPNOTSUPP) {
+        LOG(ERROR, "Cannot save a guest with vNUMA configured");
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
     dss->guest_evtchn.port = -1;
     dss->guest_evtchn_lockfd = -1;
     dss->guest_responded = 0;
-- 
2.1.4


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