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[Qemu-discuss] Help on 1G huge pages in guest

From: Surender Kumar
Subject: [Qemu-discuss] Help on 1G huge pages in guest
Date: Tue, 1 Sep 2015 08:17:36 +0000 (UTC)

  I am using a 2.6.32 linux host kernel which is running qemu-kvm version 0.12.1.  I have a guest running Ubuntu using linux kernel 3.13. The host hardware is Xeon 2680.
I am able to set up and use1G huge pages on the host with kernel bootline having the parameters default_hugepagesz=1G, hugepages=32, hugepagesz=1G. /proc/meminfo shows the correct huge page size.  There is sufficient memory on the system. When I boot the guest kernel with default_hugepagesz=1G, hugepages=32, hugepagesz=1G, the guest complains that this is “Unsupported page size of 1024m”.  If I check guest /proc/cpuinfo the  pdpe1gb flag is not set though this is part of the xml config file in virsh.
I am able to use 2M huge pages on both host and guest and can mmap and access the huge pages on both host and guest.
 I am not sure why 1G huge pages do not come up on the guest. Is this because of an old qemu-kvm version 0.12.1 being used? At this point I need to keep the host kernel version as is. Are there any workarounds to solve this problem? What probably is the root cause?

S Kumar


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