Re: [PATCH 08/16] x86: Emergency virtualization disable function

[Avi Kivity]

Eduardo Habkost wrote:
> On Thu, Nov 06, 2008 at 12:30:51PM +0200, Avi Kivity wrote:
>   
> > Eric W. Biederman wrote:
> >     
> > > > If you want to be extra simple and safe, remove kvm from the equation.  Make the
> > > > disabling code part of kdump/emergency_restart and only rely on the convention
> > > > that cr3.vmxe == vmxon.
> > > >     
> > > >         
> > > Convention?
> > >   
> > >       
> > There is a de-facto convention supported by at least vmware and kvm.  If  
> > cr4.vmxe is 1, then we are in vmx operation.  If cr4.vmxe is 0, then we  
> > are not in vmx operation.  This allows us to determine whether we need  
> > to execute vmxoff without any APIs.
> >     
>
> I am just worried about the probing needed to make sure CR4 is available
> (and that the CR4.VMXE bit means what we expect it to mean),

That's cpu_has_kvm_support() in vmx.c.  Should compile to three 
instructions.

>  before we
> try to read it and check VMXE. The same for SVM and the MSRs we need to
> touch to disable SVM.
>   

That's has_svm() in svm.c; slightly longer but not any more dangerous.

> I prefer to reuse code that already exists on KVM and is working than
> adding new probing code that I won't be able to test on all hardware
> configurations.
>   

We could move the code to a header file, and so compile it both for kvm 
and for emergency_restart/kdump.

--
error compiling committee.c: too many arguments to function

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