Re: [PATCH] Disallow setting maxmem to higher value than total physical memory size

[Michal Novotny <minovotn@redhat.com>]

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On 09/01/2010 05:20 PM, Ian Campbell wrote:
> On Wed, 2010-09-01 at 15:18 +0100, Michal Novotny wrote:
>
>    
>> Oh, ok. It's not limited to dom0 nevertheless I don't see anything to be
>> causing anything bad in domU. Of course, I can limit this to dom0 but
>> for domU you can be having e.g. this:
>> 1)
>> dom0: total memory = 8192
>> domU: memory = 4096, maxmem = 8192 (xm mem-max domU 16384 fails)
>>      
> It is useful, legal and valid to set e.g. maxmem = 12288 here, leaving
> memory = 4096. Your patch prevents that.
>
>    

That's right. I'm just saying that there's a possibility that there will 
be wrong data output from `xm list -l` command.

>> 2)
>> and when you migrate to host B:
>> dom0: total memory = 16384
>> domU: memory = 4096, maxmem = 8192
>>      
> If maxmem = 12288 then it would be possible to balloon this guest up to
> 12288 on this system. With your patch it is no longer possible. Note
> that maxmem cannot change once the domU is booted so it needs to have
> been = 12288 at the time the guest was created on Host A.
>
>    

That's correct.

>> Or should I just ignore the possibility domU maxmem could be set to
>> higher value than host machine could provide and should I limit my check
>> to dom0 only?
>>      
> Yes!
>
> I haven't considered the applicability of this patch to dom0
> particularly deeply but it is wrong to enforce this constraint on domUs.
>
> Ian.
>
>    
Ok, I'm attaching the patch now for review. Now it's working fine for 
dom0 to limit just dom0.

What do you think about this?

Michal

-- 
Michal Novotny<minovotn@redhat.com>, RHCE
Virtualization Team (xen userspace), Red Hat


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diff --git a/tools/python/xen/xend/XendDomainInfo.py b/tools/python/xen/xend/XendDomainInfo.py
index 4360ce2..aabc30f 100644
--- a/tools/python/xen/xend/XendDomainInfo.py
+++ b/tools/python/xen/xend/XendDomainInfo.py
@@ -152,6 +152,12 @@ def recreate(info, priv):
 
     assert not info['dying']
 
+    # Validate domain maxmem value not to be higher than dom0 physical memory
+    if priv:
+        total_mem = int(xc.physinfo()['total_memory'])
+        if info['maxmem_kb'] > total_mem:
+            info['maxmem_kb'] = total_mem
+
     xeninfo = XendConfig.XendConfig(dominfo = info)
     xeninfo['is_control_domain'] = priv
     xeninfo['is_a_template'] = False
@@ -1490,6 +1496,14 @@ class XendDomainInfo:
         """Set the maximum memory limit of this domain
         @param limit: In MiB.
         """
+        # Get total memory and convert to MiB
+        if self.info['is_control_domain']:
+            total_mem = int(xc.physinfo()['total_memory'] / 1024)
+
+            if limit <= 0 or limit > total_mem:
+                raise XendError('Invalid memory size, only positive values '
+                                'up to %s MiB are valid' % total_mem)
+
         log.debug("Setting memory maximum of domain %s (%s) to %d MiB.",
                   self.info['name_label'], str(self.domid), limit)
 

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