Re: [Xen-devel] [PATCH] public: there's no MMUEXT_SET_FOREIGNDOM

[Julien Grall <julien.grall@xxxxxxx>]

On 09/06/17 14:20, Julien Grall wrote:
> Hi Jan,
>
> On 08/06/17 16:19, Jan Beulich wrote:
> > Correct respective comments.
> >
> > Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> > ---
> > MMUEXT_{CLEAR,COPY}_PAGE in fact also allow to be invoked on DOMID_IO
> > owned pages at present. I've intentionally not added this to the text,
> > as I'm not sure we really mean to allow this. If we do, I think the
> > operation should also be allowed for MMIO pages not happening to have
> > an associated struct page_info.
> >
> > --- a/xen/include/public/xen.h
> > +++ b/xen/include/public/xen.h
> > @@ -550,16 +550,19 @@ DEFINE_XEN_GUEST_HANDLE(mmuext_op_t);
> >   * is useful to ensure that no mappings to the OS's own heap are
> > accidentally
> >   * installed. (e.g., in Linux this could cause havoc as reference counts
> >   * aren't adjusted on the I/O-mapping code path).
> > - * This only makes sense in MMUEXT_SET_FOREIGNDOM, but in that
> > context can
> > - * be specified by any calling domain.
> > + * This only makes sense as HYPERVISOR_mmu_update()'s and
> > + * HYPERVISOR_update_va_mapping_otherdomain()'s "foreigndom"
> > argument. For
> > + * HYPERVISOR_mmu_update() context it can be specified by any calling
> > domain,
> > + * otherwise it's only permitted if the caller is privileged.
> >   */
> >  #define DOMID_IO             xen_mk_uint(0x7FF1)
> >
> >  /*
> >   * DOMID_XEN is used to allow privileged domains to map restricted
> > parts of
> >   * Xen's heap space (e.g., the machine_to_phys table).
> > - * This only makes sense in MMUEXT_SET_FOREIGNDOM, and is only
> > permitted if
> > - * the caller is privileged.
> > + * This only makes sense as HYPERVISOR_mmu_update()'s,
> > HYPERVISOR_mmuext_op()'s,
> > + * or HYPERVISOR_update_va_mapping_otherdomain()'s "foreigndom"
> > argument, and is
> > + * only permitted if the caller is privileged.
> DOMID_XEN is used on ARM for mapping Xen buffer (e.g trace) using
s/is/will be/ as the series has not yet been merged (see [1]). But to 
clarify, xentrace is currently call xc_map_foreign_pages which will 
turned into a physmap hypercall for ARM and x86 HVM guests.
> physmap hypercall with XENMAPSPACE_foreign_gmfn_foreign.
Cheers,

[1] https://patchwork.kernel.org/patch/8604811/

--
Julien Grall

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