Re: [PATCH v3 1/5] xen/arm: Add way to disable traps on accesses to unmapped addresses

["Edgar E. Iglesias" <edgar.iglesias@gmail.com>]

On Mon, Jun 02, 2025 at 10:45:36AM +0200, Jan Beulich wrote:
> On 30.05.2025 15:45, Edgar E. Iglesias wrote:
> > --- a/xen/common/domain.c
> > +++ b/xen/common/domain.c
> > @@ -721,7 +721,8 @@ static int sanitise_domain_config(struct xen_domctl_createdomain *config)
> >           ~(XEN_DOMCTL_CDF_hvm | XEN_DOMCTL_CDF_hap |
> >             XEN_DOMCTL_CDF_s3_integrity | XEN_DOMCTL_CDF_oos_off |
> >             XEN_DOMCTL_CDF_xs_domain | XEN_DOMCTL_CDF_iommu |
> > -           XEN_DOMCTL_CDF_nested_virt | XEN_DOMCTL_CDF_vpmu) )
> > +           XEN_DOMCTL_CDF_nested_virt | XEN_DOMCTL_CDF_vpmu |
> > +           XEN_DOMCTL_CDF_trap_unmapped_accesses) )
> >      {
> >          dprintk(XENLOG_INFO, "Unknown CDF flags %#x\n", config->flags);
> >          return -EINVAL;
> > --- a/xen/include/public/domctl.h
> > +++ b/xen/include/public/domctl.h
> > @@ -66,9 +66,11 @@ struct xen_domctl_createdomain {
> >  #define XEN_DOMCTL_CDF_nested_virt    (1U << _XEN_DOMCTL_CDF_nested_virt)
> >  /* Should we expose the vPMU to the guest? */
> >  #define XEN_DOMCTL_CDF_vpmu           (1U << 7)
> > +/* Should we trap guest accesses to unmapped addresses? */
> > +#define XEN_DOMCTL_CDF_trap_unmapped_accesses  (1U << 8)
> 
> Besides being pretty long an identifier (and that's already with "guest" not
> even in the name), if this is to be arch-independent, would this perhaps fit
> x86'es recently introduced "advanced" PVH handling of holes? See [1].
> 

Looks like the implementation of the options would be related
but trap_unmapped_accesses is intended for domU's and pf-fixup is for
dom0 IIUC, so in terms of configuration they would be different...

I'm happy to change the name of trap_unmapped_accesses if there
are better (and shorter) ideas.

Thanks,
Edgar



> Jan
> 
> [1] 104591f5dd67 ("x86/dom0: attempt to fixup p2m page-faults for PVH dom0")