Re: [PATCH v3 13/16] x86/hyperlaunch: specify dom0 mode with device tree

["Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>]

On 4/10/25 07:57, Jan Beulich wrote:
> On 08.04.2025 18:07, Alejandro Vallejo wrote:
> > --- a/xen/arch/x86/domain-builder/fdt.c
> > +++ b/xen/arch/x86/domain-builder/fdt.c
> > @@ -193,6 +193,25 @@ static int __init process_domain_node(
> >               bd->domid = (domid_t)val;
> >               printk("  domid: %d\n", bd->domid);
> >           }
> > +        else if ( strncmp(prop_name, "mode", name_len) == 0 )
> > +        {
> > +            if ( fdt_prop_as_u32(prop, &bd->mode) != 0 )
> > +            {
> > +                printk("  failed processing mode for domain %s\n", name);
> > +                return -EINVAL;
> > +            }
> > +
> > +            printk("  mode: ");
> > +            if ( !(bd->mode & BUILD_MODE_PARAVIRT) )
> > +            {
> > +                if ( bd->mode & BUILD_MODE_ENABLE_DM )
> > +                    printk("HVM\n");
> > +                else
> > +                    printk("PVH\n");
> > +            }
> > +            else
> > +                printk("PV\n");
> > +        }
> My prior questions here remain: What's the significance of
> BUILD_MODE_ENABLE_DM when set alongside BUILD_MODE_PARAVIRT? What about
> any of the other bits being set?
From boot-domain.h:
                                          /* On     | Off    */
#define BUILD_MODE_PARAVIRT      (1 << 0) /* PV     | PVH/HVM */
#define BUILD_MODE_ENABLE_DM     (1 << 1) /* HVM    | PVH     */

The logic says, if BUILD_MODE_PARAVIRT bit is not set, thus an HVM 
domain, check if BUILD_MODE_ENABLE_DM has been set. This is determin if 
the domain is what the toolstack differentiates as either an HVM or PVH 
domain. As you should know, there is no case of a PV domain requiring a 
backing device mode (DM) domain. IOW, BUILD_MODE_ENABLE_DM is only 
relevant to an HVM domain.
v/r,
dps