[ kvm-Bugs-2019053 ] tbench fails on guest when AMD NPT enabled

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Bugs item #2019053, was opened at 2008-07-16 03:10
Message generated for change (Comment added) made by avik
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Category: amd
Group: None
>Status: Pending
Resolution: None
Priority: 5
Private: No
Submitted By: Alex Williamson (alex_williamson)
Assigned to: Nobody/Anonymous (nobody)
Summary: tbench fails on guest when AMD NPT enabled

Initial Comment:
Running on a dual-socket system with AMD 2356 quad-core processors (8 total cores), 32GB RAM, Ubuntu Hardy 2.6.24-19-generic (64bit) with kvm-71 userspace and kernel modules.  With no module options, dmesg confirms: kvm: Nested Paging enabled

Start guest with:

/usr/local/kvm/bin/qemu-system-x86_64 -hda /dev/VM/Ubuntu64 -m 1024 -net nic,model=e1000,mac=de:ad:be:ef:00:01 -net tap,script=/root/bin/br0-ifup -smp 8 -vnc :0

Guest VM is also Ubuntu Hardy 64bit.  On the guest run 'tbench 16 <tbench server>'.  System running tbench_srv is a different system in my case.

The tbench client will fail randomly, often quietly with "Child failed with status 1", but sometimes more harshly with a glibc double free error.

If I unload the modules and reload w/o npt:

modprobe -r kvm-amd
modprobe -r kvm
modprobe kvm-amd npt=0

dmesg confirms: kvm: Nested Paging disabled

The tbench test now runs over and over successfully.  The test also runs fine on an Intel E5450 (no EPT).

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>Comment By: Avi Kivity (avik)
Date: 2008-07-16 17:19

Message:
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Strange.  If you add an mlockall() to qemu startup, does the test pass?

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