Re: [PATCH v10 7/8] KVM: PPC: Implement H_SVM_INIT_ABORT hcall

Ram Pai
2019-11-13T06:32:33Z

On Wed, Nov 13, 2019 at 11:14:27AM +1100, Paul Mackerras wrote:
> On Tue, Nov 12, 2019 at 06:45:55AM -0800, Ram Pai wrote:
> > On Tue, Nov 12, 2019 at 10:32:04PM +1100, Paul Mackerras wrote:
> > > On Mon, Nov 11, 2019 at 11:52:15PM -0800, Ram Pai wrote:
> > > > There is subtle problem removing that code from the assembly.
> > > >
> > > > If the H_SVM_INIT_ABORT hcall returns to the ultravisor without clearing
> > > > kvm->arch.secure_guest, the hypervisor will continue to think that the
> > > > VM is a secure VM. However the primary reason the H_SVM_INIT_ABORT
> > > > hcall was invoked, was to inform the Hypervisor that it should no longer
> > > > consider the VM as a Secure VM. So there is a inconsistency there.
> > >
> > > Most of the checks that look at whether a VM is a secure VM use code
> > > like "if (kvm->arch.secure_guest & KVMPPC_SECURE_INIT_DONE)". Now
> > > since KVMPPC_SECURE_INIT_ABORT is 4, an if statement such as that will
> > > take the false branch once we have set kvm->arch.secure_guest to
> > > KVMPPC_SECURE_INIT_ABORT in kvmppc_h_svm_init_abort. So in fact in
> > > most places we will treat the VM as a normal VM from then on. If
> > > there are any places where we still need to treat the VM as a secure
> > > VM while we are processing the abort we can easily do that too.
> >
> > Is the suggestion -- KVMPPC_SECURE_INIT_ABORT should never return back
> > to the Ultravisor? Because removing that assembly code will NOT lead the
>
> No. The suggestion is that vcpu->arch.secure_guest stays set to
> KVMPPC_SECURE_INIT_ABORT until userspace calls KVM_PPC_SVM_OFF.

In the fast_guest_return path, if it finds
(kvm->arch.secure_guest & KVMPPC_SECURE_INIT_ABORT) is true, should it return to
UV or not?

Ideally it should return back to the ultravisor the first time
KVMPPC_SECURE_INIT_ABORT is set, and not than onwards.

RP