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

[Michal Novotny <minovotn@xxxxxxxxxx>]

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@xxxxxxxxxx>, RHCE
Virtualization Team (xen userspace), Red Hat

Attachment: xen-disallow-setting-max-mem-higher-than-total-phys-mem.patch
Description: Text Data

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