Re: [Xen-devel] [PATCH] Prevent changing a memory size of Domain-0even if users make a careless mistake

[Masaki Kanno <kanno.masaki@xxxxxxxxxxxxxx>]

Sat, 5 Apr 2008 19:36:07 +0100, Mark Williamson wrote:

>> I think it's fair to just say "Don't do that then, you idiot!". :-)
>
>I think if we have a "dom0-min-mem" parameter then we may as well use it 
>consistently.  We already use it to prevent event quite determined 
>foot-shooting attempts (like starting up too many domains!).
>
>Seems consistent to apply the rule whenever an xm command might balloon dom0.
>
>Kan, a comment on your patch:
>
>
>diff -r db943e8d1051 tools/python/xen/xend/XendDomainInfo.py
>--- a/tools/python/xen/xend/XendDomainInfo.py   Tue Apr 01 10:09:33 2008 +
>0100
>+++ b/tools/python/xen/xend/XendDomainInfo.py   Fri Apr 04 13:43:55 2008 +
>0900
>@@ -986,6 +986,14 @@ class XendDomainInfo:
>                   self.info['name_label'], str(self.domid), target)
>         
>         MiB = 1024 * 1024
>+
>+        if self.domid == 0:
>+            dom0_min_mem = xoptions.get_dom0_min_mem()
>+            memory_cur = self.get_memory_dynamic_max() / MiB
>+            if target < memory_cur:
>+                if dom0_min_mem == 0 or dom0_min_mem > target:
>
>If I recall correctly, the current meaning of dom0_min_mem set to 0 is "No 
>limiting", so I think you can just remove that check to be consistent with 
>existing behaviour.

Hi Mark,

Is it?  As far as I know, the current meaning of dom0-min-mem set to 0 
is "No ballooning".  There are the following comments about dom0-min-mem 
in xend-config.sxp. 

# Dom0 will balloon out when needed to free memory for domU.
# dom0-min-mem is the lowest memory level (in MB) dom0 will get down to.
# If dom0-min-mem=0, dom0 will never balloon out.

Best regards,
 Kan

>
>Cheers,
>Mark
>
>+                    raise XendError("memory_dynamic_max cannot be changed 
>for 
>safety reasons")
>+
>         self._safe_set_memory('memory_dynamic_min', target * MiB)
>         self._safe_set_memory('memory_dynamic_max', target * MiB)
> 
>
>
>>  -- Keir
>>
>> On 4/4/08 11:06, "Masaki Kanno" <kanno.masaki@xxxxxxxxxxxxxx> wrote:
>> > Hi,
>> >
>> > If users accidentally change a memory size of Domain-0 to very small
>> > memory size by xm mem-set command, users will be not able to operate
>> > Domain-0.  I think that Domain-0 is important for Xen, so I'd like to
>> > prevent the accident by xm mem-set command.
>> >
>> > This patch prevents changing the memory size of Domain-0 by xm mem-set
>> > command if specified memory size is smaller than dom0-min-mem in
>> > xend-config.sxp.
>> >
>> >  # cat /etc/xen/xend-config.sxp | grep "(dom0-min-mem"
>> >  (dom0-min-mem 384)
>> >  # xm list Domain-0
>> >  Name                                        ID   Mem VCPUs      State
>> > Time(s)
>> >  Domain-0                                     0   941     2     r-----
>> > 62.6
>> >  # xm mem-set Domain-0 1
>> >  Error: memory_dynamic_max cannot be changed for safety reasons
>> >  Usage: xm mem-set <Domain> <Mem>
>> >
>> >  Set the current memory usage for a domain.
>> >  # xm list Domain-0
>> >  Name                                        ID   Mem VCPUs      State
>> > Time(s)
>> >  Domain-0                                     0   941     2     r-----
>> > 63.6
>> >
>> >
>> > Signed-off-by: Masaki Kanno <kanno.masaki@xxxxxxxxxxxxxx>
>> >
>> > Best regards,
>> >  Kan
>> >
>> > _______________________________________________
>> > Xen-devel mailing list
>> > Xen-devel@xxxxxxxxxxxxxxxxxxx
>> > http://lists.xensource.com/xen-devel
>>
>> _______________________________________________
>> Xen-devel mailing list
>> Xen-devel@xxxxxxxxxxxxxxxxxxx
>> http://lists.xensource.com/xen-devel
>
>
>
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>
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