[Xen-devel] [PATCH for-4.7] libxl: keep PoD target adjustment by memory fudge after reload_domain_config()

[Wei Liu <wei.liu2@xxxxxxxxxx>]

From: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>

Commit 56fb5fd623 ("libxl: adjust PoD target by memory fudge, too")
introduced target_memkb adjustment for HVM PoD domains on create. The
adjustment is however being reset on reload_domain_config() (e.g. when
we reboot the guest). For example:

I'm trying to create HVM PoD domain with the following settings:
memory=1024
maxmem=4096
When the domain boots for the first time I see the following in Xen:

(XEN)     nr_pages=262145 ... max_pages=262400 (looks good)

When I reboot the domain I see the following:
(XEN)     nr_pages=261889 ... max_pages=262144  (oops)

After second reboot:
(XEN)     nr_pages=261633 ... max_pages=261888 (even less)

And eventually the domain crashes with "p2m_pod_demand_populate: Dom4 out of
PoD memory! (tot=261377 ents=787200 dom4)".

Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
---
 tools/libxl/libxl.c          |  8 ++++----
 tools/libxl/libxl_dom.c      | 10 ++--------
 tools/libxl/libxl_internal.h | 15 +++++++++++++++
 3 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index b9d855b..5aaf02d 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -7229,12 +7229,12 @@ int libxl_retrieve_domain_configuration(libxl_ctx *ctx, 
uint32_t domid,
             LOG(ERROR, "fail to get memory target for domain %d", domid);
             goto out;
         }
-        /* Target memory in xenstore is different from what user has
-         * asked for. The difference is video_memkb. See
-         * libxl_set_memory_target.
+
+        /* libxl__get_targetmem_difference() calculates the difference from
+         * what is in xenstore to what we have in the domain build info.
          */
         d_config->b_info.target_memkb = target_memkb +
-            d_config->b_info.video_memkb;
+            libxl__get_targetmem_difference(gc, &d_config->b_info);
 
         d_config->b_info.max_memkb = max_memkb;
     }
diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
index 9b20cf5..20fd458 100644
--- a/tools/libxl/libxl_dom.c
+++ b/tools/libxl/libxl_dom.c
@@ -490,7 +490,6 @@ int libxl__build_post(libxl__gc *gc, uint32_t domid,
     xs_transaction_t t;
     char **ents;
     int i, rc;
-    int64_t mem_target_fudge;
 
     if (info->num_vnuma_nodes && !info->num_vcpu_soft_affinity) {
         rc = set_vnuma_affinity(gc, domid, info);
@@ -523,17 +522,12 @@ int libxl__build_post(libxl__gc *gc, uint32_t domid,
         }
     }
 
-    mem_target_fudge =
-        (info->type == LIBXL_DOMAIN_TYPE_HVM &&
-         info->max_memkb > info->target_memkb)
-        ? LIBXL_MAXMEM_CONSTANT : 0;
-
     ents = libxl__calloc(gc, 12 + (info->max_vcpus * 2) + 2, sizeof(char *));
     ents[0] = "memory/static-max";
     ents[1] = GCSPRINTF("%"PRId64, info->max_memkb);
     ents[2] = "memory/target";
-    ents[3] = GCSPRINTF("%"PRId64, info->target_memkb - info->video_memkb
-                        - mem_target_fudge);
+    ents[3] = GCSPRINTF("%"PRId64, info->target_memkb -
+                        libxl__get_targetmem_difference(gc, info));
     ents[4] = "memory/videoram";
     ents[5] = GCSPRINTF("%"PRId64, info->video_memkb);
     ents[6] = "domid";
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index fac5751..59df53d 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -4107,6 +4107,21 @@ static inline void libxl__update_config_vtpm(libxl__gc 
*gc,
     libxl_uuid_copy(CTX, &dst->uuid, &src->uuid);
 }
 
+/* Target memory in xenstore is different from what user has
+ * asked for. The difference is video_memkb + (possible) fudge.
+ * See libxl_set_memory_target.
+ */
+static inline
+uint64_t libxl__get_targetmem_difference(libxl__gc *gc,
+                                         const libxl_domain_build_info *info)
+{
+    int64_t mem_target_fudge = (info->type == LIBXL_DOMAIN_TYPE_HVM &&
+                                info->max_memkb > info->target_memkb)
+                                ? LIBXL_MAXMEM_CONSTANT : 0;
+
+    return info->video_memkb + mem_target_fudge;
+}
+
 /* Macros used to compare device identifier. Returns true if the two
  * devices have same identifier. */
 #define COMPARE_DEVID(a, b) ((a)->devid == (b)->devid)
-- 
2.1.4


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