Re: [Xen-devel] [PATCH] Nested VMX: CR emulation fix up

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 10/09/2013 08:31 PM, Zhang, Yang Z wrote:
> Boris Ostrovsky wrote on 2013-10-09:
> > On 10/09/2013 03:28 AM, Zhang, Yang Z wrote:
> > > Boris Ostrovsky wrote on 2013-10-08:
> > > > On 10/08/2013 04:31 AM, Jan Beulich wrote:
> > > >
> > > > > Considering that this touches code common with nested SVM, I'd
> > > > > expect the SVM maintainers to have to approve of the change in any case.
> > > > >
> > > > > In particular I wonder whether this addition isn't obsoleting
> > > > > SVM's ns_cr0.
> > > > I am not sure whether ns_cr0 (replaced with nv_guest_cr[0]) would
> > > > then be updated in paths where it currently is not.
> > > >
> > > > For example in nsvm_vmcb_prepare4vmrun():
> > > >
> > > >        /* CR0 */ svm->ns_cr0 = v->arch.hvm_vcpu.guest_cr[0]; cr0 =
> > > >        nestedsvm_fpu_vmentry(svm->ns_cr0, ns_vmcb, n1vmcb, n2vmcb);
> > > >        v->arch.hvm_vcpu.guest_cr[0] = ns_vmcb->_cr0; rc =
> > > >        hvm_set_cr0(cr0);  <------ nv_guest_cr[0] will get set here.
> > > I am not familiar with SVM code. If you think this change may impact
> > > the
> > nested SVM. Then I will move the change to VMX specific code.
> >
> > No, it doesn't affect SVM code. I was responding to Jan's suggestion
> > to replace SVM's ns_cr0 with the new guest_cr[0].
> So is it ok to change the code according Jan's suggestion?
No. My point was that there may be unintended consequences to the change and
you should leave ns_cr0 alone.


-boris

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