Description of problem:
After memory resizing within PV guest via balloon, the "xm list -l" still shows the memory size before balloon

Version-Release number of selected component (if applicable):
xen-3.0.3-132.el5
rhel5 PV guest

How reproducible:
100%

Steps to Reproduce:

1. Start a RHEL5 PV guest, and read from /proc/xen/balloon in guest.
[guest]# cat /proc/xen/balloon
current allocation:  1048576 kB
Requested target:    1048576 kB
Low-mem balloon:        8192 kB
High-mem balloon:          0 kB
Driver pages:              0 kB
Xen hard limit:          ??? kB

2.Lower memory size of PV guest via balloon. In the guest:
[guest]# echo 512M > /proc/xen/balloon
[guest]# cat /proc/xen/balloon
Current allocation:   524288 kB
Requested target:     524288 kB
Low-mem balloon:      532480 kB
High-mem balloon:          0 kB
Driver pages:              0 kB
Xen hard limit:          ??? kB
[guest]# free -m
             total       used       free     shared    buffers     cached
Mem:           512        322        189          0         15        161
-/+ buffers/cache:        145        366
Swap:          588          0        588

3. Check memory size of PV guest externally.
[host]# xm list
Name                                      ID Mem(MiB) VCPUs State   Time(s)
Domain-0                                   0     3779     4 r-----   1924.2
RHEL5.7-64-PV                             47      512     4 -b----     11.3
[host]# xm list -l 47| grep mem
    (memory 1024)
    (shadow_memory 0)
    (maxmem 1024)

  
Actual results:
The memory info from "xm list -l" still remains 1024

Expected results:
The memory info from "xm list -l" should change to 512.

Additional info:
Also can be reproduced on xen-3.0.3-120.el5
The guest mem-set from Domain0 works well.