Re: [libvirt] [BUG] mlock support breakage
On Mon, Mar 13, 2017 at 12:35:42PM -0400, Luiz Capitulino wrote:
On Mon, 13 Mar 2017 16:08:58 +0000
"Daniel P. Berrange" <berrange(a)redhat.com> wrote:
> > 2. Drop change c2e60ad0e51 and automtically increase memory
> > locking limit to infinity when seeing <memoryBacking><locked/>
> >
> > pros: make all cases work, no more <hard_limit> requirement
> >
> > cons: allows guests with <locked/> to lock all memory
> > assigned to them plus QEMU allocations. While this seems
> > undesirable or even a security issue, using <hard_limit>
> > will have the same effect
>
> I think this is the only viable approach, given that no one can
> provide a way to reliably calculate QEMU peak memory usage.
> Unless we want to take guest RAM + $LARGE NUMBER - eg just blindly
> assume that 2 GB is enough for QEMU working set, so for an 8 GB
> guest, just set 10 GB as the limit.
Better to set it to infinity and be done with it.
Not neccessarily, no. If we set $RAM + $LARGE_NUMBER, we are still likely
to be well below the overall physical RAM of a host. IOW, a single
compromised QEMU would still be restricted in how much it can pin. If we
set it to infinity then a compromised QEMU can lock all of physical RAM
doing a very effective DOS on the host, as it can't even swap the guest
out to recover.
Regards,
Daniel
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