Re: Nested kvm_intel broken on pre 3.3 hosts

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On Wed, Aug 01, 2012 at 01:29:11PM +0200, Stefan Bader wrote:
> I have been looking at a report[1] about the kvm_intel module failing to load on
> linux v3.3 and newer guests when running on a v3.2 host. Bisection turned up the
> following patch:
> 
> commit fee84b079d5ddee2247b5c1f53162c330c622902
> Author: Avi Kivity <avi@xxxxxxxxxx>
> Date:   Thu Nov 10 14:57:25 2011 +0200
> 
>     KVM: VMX: Intercept RDPMC
> 
>     Intercept RDPMC and forward it to the PMU emulation code.
> 
>     Signed-off-by: Avi Kivity <avi@xxxxxxxxxx>
>     Signed-off-by: Gleb Natapov <gleb@xxxxxxxxxx>
>     Signed-off-by: Avi Kivity <avi@xxxxxxxxxx>
> 
> It looks like requiring the feature based on cpu fails when the host (outer kvm
> module) code does not support it. So maybe that should be optional instead of
> required?
According to Intel SDM there was never CPU that didn't support RDPMC
exiting. Looks like unfortunate nested VMX bug.

> Seems also like kvm_amd does not "suffer" from any test that could fail and
> should be ok (though I did not test it personally).
> 
> -Stefan
> 
> [1] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1031090
> 



--
			Gleb.
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