qemu with kvm is extremly slow in 2.6.34.1.

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qemu with kvm is extremly slow in 2.6.34.1.

Postby username » Tue Jul 13, 2010 4:15 am

- qemu-kvm 0.12.4
- kernel 2.6.34.1
- grsecurity 2.2.0-2.6.34.1-201007101507
- gentoo hardened from anarchy overlay [1].
- amd64

qemu-kvm is very slow and produces 100% load on one core. I can even see the bios printing single characters. The problem first occured in an ebuild after 2.6.33. 2.6.33-r1 does not work anymore. [2] is the commit from 2.6.33 to 2.6.33-r1. The problem seems to be related to work done between 2.1.14-2.6.33-201003071645 (2.6.33) and 2.1.14-2.6.33.2-201004071936 (2.6.33-r1) or between kernel 2.6.33 and 2.6.33.2 (contained in 2.6.33-r1). The patches of gentoo have not changed between 2.6.33 and 2.6.33-r1.

[1] http://git.overlays.gentoo.org/gitweb/?p=dev/anarchy.git;a=tree;f=sys-kernel/hardened-sources;h=b355c2d5b4498ba992f66d7372662fbe83c224e0;hb=HEAD
[2] http://git.overlays.gentoo.org/gitweb/?p=proj/hardened-dev.git;a=commit;h=9e3c62080f1be0d1615694d9b79e1fb5e233b45a

I hope that helps to find the problem. I do not use UDEREF.
Last edited by username on Fri Jul 16, 2010 9:02 am, edited 1 time in total.
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Re: qemu with kvm is extremly slow in 2.6.34.1.

Postby username » Tue Jul 13, 2010 4:16 am

Sorry for the wrong board. :-(
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Re: qemu with kvm is extremly slow in 2.6.34.1.

Postby PaX Team » Fri Jul 16, 2010 6:05 pm

username wrote:The problem seems to be related to work done between 2.1.14-2.6.33-201003071645 (2.6.33) and 2.1.14-2.6.33.2-201004071936 (2.6.33-r1) or between kernel 2.6.33 and 2.6.33.2 (contained in 2.6.33-r1).
what changed in PaX in that timeframe was the introduction of UDEREF for amd64. did you perhaps enable it? if you did, try booting with pax_nouderef and see if it helps (in general, read its config help, it's not a 'free' feature on amd64, unfortunately).
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Re: qemu with kvm is extremly slow in 2.6.34.1.

Postby konst » Fri Jul 16, 2010 9:43 pm

PaX Team wrote:
username wrote:The problem seems to be related to work done between 2.1.14-2.6.33-201003071645 (2.6.33) and 2.1.14-2.6.33.2-201004071936 (2.6.33-r1) or between kernel 2.6.33 and 2.6.33.2 (contained in 2.6.33-r1).
what changed in PaX in that timeframe was the introduction of UDEREF for amd64. did you perhaps enable it? if you did, try booting with pax_nouderef and see if it helps (in general, read its config help, it's not a 'free' feature on amd64, unfortunately).


Haven't tried it yet but in the help screen it says if you have hardware assisted virtualization there shouldn't be a slowdown.
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Re: qemu with kvm is extremly slow in 2.6.34.1.

Postby PaX Team » Fri Jul 16, 2010 10:07 pm

konst wrote:Haven't tried it yet but in the help screen it says if you have hardware assisted virtualization there shouldn't be a slowdown.
the help wasn't updated for the amd64 version since it's kinda experimental still, better read the announcement email on the list about what to expect ;).
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Re: qemu with kvm is extremly slow in 2.6.34.1.

Postby username » Sat Jul 17, 2010 7:41 am

As I said before, I do not use UDEREF at all. It is disabled in the kernel configuration. I tried to boot with the kernel parameter, but it did not solve the problem. I don't understand, that nobody else has the same problem. I do not configure PaX or grsec myself. I use the predefined profiles from hardened gentoo. Is there anything else, I need to disable in the kernel configuration?
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Re: qemu with kvm is extremly slow in 2.6.34.1.

Postby PaX Team » Sat Jul 17, 2010 10:30 am

username wrote:As I said before, I do not use UDEREF at all.
oh sorry, i missed it, must be the heat ;).
Is there anything else, I need to disable in the kernel configuration?
yes, do you have KERNEXEC enabled? it enables the common infrastructure used by UDEREF as well and can cause the slowdown.
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Re: qemu with kvm is extremly slow in 2.6.34.1.

Postby Jorge » Thu Sep 22, 2011 4:08 am

oh, i've been searching for the same issue and came across boardreader.com/thread/Hardened_kernel_2_6_38_and_latest_qemu_k_1mboX210.html. Thanks you too, for providing some hints in order to solve the slow speed of qemu+kvm!
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Re: qemu with kvm is extremly slow in 2.6.34.1.

Postby PaX Team » Tue Sep 18, 2012 5:58 am

as of yesterday, this problem should be fixed finally.
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