On Thu, Aug 05, 2010 at 01:41:16PM +0200, Moritz Duge wrote: > Hi, > I had some trouble while using the ballooning feature of KVM (using > Ubuntu 10.04 with standard software versions). > > > The first scenario: > 1. Having a guest started by this command: qemu -enable-kvm -m 768 > -balloon virtio -cdrom linux_2.6.34.iso > The guest is running Linux 2.6.34 including the ballooning driver. > 2. Entering "balloon 256" and a few seconds later "info balloon" in > the Qemu monitor. Qemu will report, the guest uses 256mb of memory > now. The guest is reporting the same (using "free" for example). > 3. Entering "change ide1-cd0 linux_2.6.18.iso" to change the guests > CD-ROM to another image, containing a Linux kernel without > ballooning driver. > 4. Rebooting the guest. > 5. After booting the 2.6.18-OS, it will report it has 768mb memory > (using "free). But Qemu monitor will still tell 256, when entering > "info memory". > I know why this happens. But is this a good behaviour? Shouldn't > Qemu tell something like "maybe 256, but there is no more balloon > driver in the guest and maybe it uses the full 768 now"??? What version of qemu-kvm are you using? Reporting should work properly with a recent qemu-kvm version. > The second scenario: > After the first scenario, the guest can also really start using the > additional 512mb of memory (768 - 256)!!! I think this shouldn't > happen or at least there should be an option to allow or deny this. > Or at least least least this should be printed in big letters in the > man-pages or somewhere else where everyone will read it! > Because before I experienced this, I assumed I can be sure the guest > can't get back the memory which was freed using ballooning. So if I > use the memory freed by ballooning for some other qemu-instances and > the first one starts to use those memory again, all Qemu instances > will crash (this is what actually happens in most cases). > What I'm asking for, is a way to force the guest to stay in the > memory I assigned by ballooning. And if the guest tries to use more > memory (maybe because it just unloaded the ballooning driver) the > guest should crash, but the host shouldn't get in any trouble!!! > This can be really annoying. I think a very common use-case for > virtualization is, to run untrusted software or unsecure webservices > in a vm, so the bad software can't do anything to the host or other > VMs on the host. But when using ballooning, the bad software can! > It's no "remote code execution", but the guest can consume a lot of > memory and cause the host or at least the other VMs on the host to > crash. Ballooning requires guest cooperation. If you want to enforce memory limits, take a look at cgroups (Documentation/cgroups/memory.txt in the kernel source tree). > > > The third scenario: > 1. Booting a machine with a guest not having a ballooning driver. > (e.g. qemu -enable-kvm -m 768 -balloon virtio -cdrom > linux_2.6.18.iso) > 2. Adjusting the memory by "balloon 512" in the qemu monitor. > 3. Qemu won't report that it couldn't adjust the memory. Instead it > will wait until the guest loads a ballooning driver. Is this a good > behaviour? Shouldn't there be at least a switch in the qemu monitor > for the command "balloon". So if I use the switch when changing the > memory (e.g. "balloon -h 256"), qemu won't try to change the memory > later and it will tell me "error: no ballooning driver found". You see that that guest has not ballooned down with the output from "info balloon". > > Thanks for reading and thanks a lot, if there will be a solution for > this, specially for scenario two. > > Greetings > Moritz Duge > > -- > Artfiles New Media GmbH | Heidenkampsweg 100 | 20097 Hamburg > Tel: 040 - 32 02 72 90 | Fax: 040 - 32 02 72 95 > E-Mail:support@xxxxxxxxxxx | Web:http://www.artfiles.de > Geschäftsführer: Carsten Bals | Harald Oltmanns | Tim Evers > Eingetragen im Handelsregister Hamburg - HRB 81478 > > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
