Re: [PATCH] KVM: PPC: Book3S HV: Add a capability for enabling secure guests

[Paul Mackerras <paulus@ozlabs.org>]

On Thu, Mar 19, 2020 at 12:41:08PM -0700, Ram Pai wrote:
> On Thu, Mar 19, 2020 at 03:33:01PM +1100, Paul Mackerras wrote:
[snip]
> > --- a/arch/powerpc/kvm/powerpc.c
> > +++ b/arch/powerpc/kvm/powerpc.c
> > @@ -670,6 +670,11 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> >  		     (hv_enabled && cpu_has_feature(CPU_FTR_P9_TM_HV_ASSIST));
> >  		break;
> >  #endif
> > +#if defined(CONFIG_KVM_BOOK3S_HV_POSSIBLE) && defined(CONFIG_PPC_UV)
> > +	case KVM_CAP_PPC_SECURE_GUEST:
> > +		r = hv_enabled && !!firmware_has_feature(FW_FEATURE_ULTRAVISOR);
> 
> We also need to check if the kvmppc_uvmem_init() has been successfully
> called and initialized.
> 
> 	r = hv_enabled && !!firmware_has_feature(FW_FEATURE_ULTRAVISOR)
> 		&& kvmppc_uvmem_bitmap;

Well I can't do that exactly because kvmppc_uvmem_bitmap is in a
different module (the kvm_hv module, whereas this code is in the kvm
module), and I wouldn't want to depend on kvmppc_uvmem_bitmap, since
that's an internal implementation detail.

The firmware_has_feature(FW_FEATURE_ULTRAVISOR) test ultimately
depends on there being a device tree node with "ibm,ultravisor" in its
compatible property (see early_init_dt_scan_ultravisor()).  So that
means there is an ultravisor there.  The cases where that test would
pass but kvmppc_uvmem_bitmap = NULL would be those where the device
tree nodes are present but not right, or where the host is so short of
memory that it couldn't allocate the kvmppc_uvmem_bitmap.  If you
think those cases are worth worrying about then I will have to devise
a way to do the test without depending on any symbols from the kvm-hv
module.

Paul.