RE: [PATCH 05/12] x86/hyperv: Change vTOM handling to use standard coco mechanisms

[Michael Kelley (LINUX)]

From: Tianyu Lan <ltykernel@xxxxxxxxx> Sent: Thursday, November 3, 2022 7:01 AM
> 
> On 10/21/2022 1:57 AM, Michael Kelley wrote:
> > +
> > +void __init hv_vtom_init(void)
> > +{
> > +	cc_set_vendor(CC_VENDOR_HYPERV);
> > +	cc_set_mask(ms_hyperv.shared_gpa_boundary);
> > +	physical_mask &= ms_hyperv.shared_gpa_boundary - 1;
> 
> 
> hv_vtom_init() also works for VBS case. VBS doesn't have vTOM support
> and so shared_gpa_boundary should not be applied for VBS. Here seems to
> assume ms_hyperv.shared_gpa_boundary to 0 for VBS, right?

Yes, that is correct.  In fact, you'll notice that this patch slightly changes
the code in ms_hyperv_init_platform() so that shared_gpa_boundary is
set only when it is known to be valid; otherwise it is left as zero.  This
change is specifically so that shared_gpa_boundary is zero for the VBS
case.

Michael