Running a KVM guest with > 3.5 GB of RAM

Submitted by thijs on 7 April, 2009 - 14:20

We've been running KVM for a while now, but only last week I noticed that the guests I had running with more than 3.5GB of RAM somehow didn't see more than those 3.5. While booting, the following message is displayed: 'WARNING: BIOS bug: CPU MTRRs don't cover all of memory, losing xxxMB of RAM.' along whith a stacktrace. KVM depends on the Bochs bios, which apparently doesn't support this amount of memory. Or rather didn't, because an updated bios is available in the Bochs cvs. Just checkout the bochs/bios/BIOS-bochs-latest and replace the /usr/share/kvm/bios.bin (at least that's where it is on Ubuntu). Stop and start the guests (a restart doesn't update the bios) and the amount of RAM is detected properly.

Update: The BIOS I used above seems to have a problem with the network connection. The VMs send out a DHCP request but do not accept the offer returned by the DHCP server. I solved this by using BIOS-bochs-kvm from this rpm.

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