Re: [PATCH 1/2] vmx,svm: Add module parameter to ignore the 'in use' check

[Sasha Levin <levinsasha928@gmail.com>]

On Tue, 2011-07-05 at 12:37 +0300, Avi Kivity wrote:
> On 07/05/2011 12:32 PM, Sasha Levin wrote:
> > On Tue, 2011-07-05 at 11:11 +0200, Joerg Roedel wrote:
> > >  On Tue, Jul 05, 2011 at 11:14:43AM +0300, Sasha Levin wrote:
> > >  >  I have no information about the machine.  It was the result of trying
> > >  >  to debug an issue reported on IRC where we found that the SVM flag is
> > >  >  being set after boot even before the kvm module is loaded.
> > >
> > >  Have you ruled out that any other third-party hypervisor module was
> > >  loaded before KVM? The virtual-box module for example?
> >
> > No other hypervisor was installed and lsmod output was clean.
> 
> This needs to be understood further.
> 

Please note that I don't have access to the hardware in question, this
was done over IRC.

Here are the steps taken in debugging this issue:

1. Looking at the dmesg ( http://pastebin.com/eM7bDY8r ) we saw that
when trying to load the kvm module, the following error shows up: 'kvm:
enabling virtualization on CPU0 failed'.

2. We went through the lsmod output (unfortunately I don't have the link
as it's gone from my IRC buffer) and didn't see any modules belonging to
other hypervisors.

3. At that point, looking at the code - we figured that a set SVM flag
is the possible culprit since it's the only code path which fails
loading the module with that error message without printing anything
else.

4. Installed msr-tools and injected the msr module so that we could read
msr values from userspace.

5. Ran 'rdmsr 0xc0000080' to read the extended feature register. The
output had bit 12 set - which means that SVM bit was enabled.

6. Ran 'wrmsr 0xc0000080 0xd01' which disabled the SVM bit.

7. kvm module loaded ok.

-- 

Sasha.