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Re: [Xen-users] amd processors + virtualisation

To: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
Subject: Re: [Xen-users] amd processors + virtualisation
From: Thomas Harold <tgh@xxxxxxxxxxxx>
Date: Tue, 29 May 2007 12:08:33 -0400
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Petersson, Mats wrote:
On the newer CentOS5 boxes using AM2 Athlon64 X2 and SocketF Opteron CPUs, the default CentOS5 kernel does allow the "svm" flag to peek through. And I have not installed virtualization support on this box (yet).

Presumably, you have a recent enough kernel now (it's been in there for
quite some time, I spent a few minutes trying to locate the version
where it went in, but I (using google) wasn't able to find it...)

Ah, that makes sense.  (Goes poking through his session logs...)

Here's the original install, probably using Gentoo 2006.0 w/ the 2.6.15 kernel (but Gentoo's version). As you can see, the grep didn't find the "svm" flag.

livecd ~ # cat /proc/cpuinfo | grep 'flags'
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mm
xext fxsr_opt lm 3dnowext 3dnow pni cx16 lahf_lm cmp_legacy

livecd ~ # cat /proc/cpuinfo | grep 'svm'
livecd ~ # cat /proc/version
Linux version 2.6.15-gentoo-r5 (root@poseidon) (gcc version 3.4.4 (Gentoo 3.4.4-r1, ssp-3.4.4-1.0, pie-8.7.8)) #1 SMP Tue Feb 21 17:
19:47 UTC 2006
livecd ~ #

Here's an entry from the next day after upgrading to 2.6.17. This one shows the "svm" flag.

azure ~ # cat /proc/version
Linux version 2.6.17-gentoo-r4 (root@livecd) (gcc version 3.4.4 (Gentoo 3.4.4-r1, ssp-3.4.4-1.0, pie-8.7.8)) #1 SMP Sat Aug 26 00:34
:30 EDT 2006

livecd ~ # cat /proc/cpuinfo | grep 'flags'
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mm
xext fxsr_opt lm 3dnowext 3dnow pni cx16 lahf_lm cmp_legacy svm cr8_legacy

So it was probably either 2.6.16 or 2.6.17 where the code for the "svm" flag was added.

...

I wasn't sure how the kernel detected those flags. I didn't know whether it was special detection code (which had to be updated for new features) or whether the processor spit back a string listing.

Thanks for the responses.

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