[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] libxc: try to find last used pfn when migrating
On 27/11/15 16:22, Ian Jackson wrote: > Juergen Gross writes ("Re: [Xen-devel] [PATCH] libxc: try to find last used > pfn when migrating"): >> xl migrate will use much less resources for a domain with a 3.x kernel >> started with max_mem being much larger than mem. E.g. in case you start >> a domain on a small stand-by system and migrate it later to the large >> production system and want to balloon it up there. >> >> Additionally there was a discussion this week on irc regarding this >> topic and concern was raised this could block dom0 responsiveness. > > I agree that this is a real problem but AFAICT I don't think the > approach taken in Juergen's toolstack patch will solve it completely. > > I would phrase the bug like this: > > A malicious guest kernel can cause the toolstack, when attempting > to migrate the domain, to use wildly excessive dom0 RAM. > > I think where the administrator has configured a guest with (say) 1G > of RAM, the memory used by the toolstack to migrate it should be > significantly less than that 1G. > > If the toolstack algorithms are such that strange behaviour by a guest > could violate this assumption, then the toolstack should have an > explicit check and (by default, at least) refuse to migrate such a > guest. > > I think Juergen's patch is a good workaround for existing guests which > /accidentally/ exhibit undesirable behaviour, if we want to keep > supporting them. It should be considered to be a working base for being able to reject migrating a misbehaving domain. I guess any pv-guest which active p2m list is covering more than twice it's max_mem can be considered to be misbehaving and migration could be rejected. More fine tuning would be possible by supporting a sparse p2m list, but this would require more work. I'm not sure if it's possible to support a sparse logdirty bitmap with current hypervisor interfaces. Juergen _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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