Re: [RFC PATCH V1 04/12] xen/arm: Introduce arch specific bits for IOREQ/DM features

[Julien Grall <julien@xxxxxxx>]

Hi Paul,

On 04/08/2020 08:49, Paul Durrant wrote:
> > diff --git a/tools/libxc/xc_dom_arm.c b/tools/libxc/xc_dom_arm.c
> > index 931404c..b5fc066 100644
> > --- a/tools/libxc/xc_dom_arm.c
> > +++ b/tools/libxc/xc_dom_arm.c
> > @@ -26,11 +26,19 @@
> >   #include "xg_private.h"
> >   #include "xc_dom.h"
> >
> > -#define NR_MAGIC_PAGES 4
> > +
> >   #define CONSOLE_PFN_OFFSET 0
> >   #define XENSTORE_PFN_OFFSET 1
> >   #define MEMACCESS_PFN_OFFSET 2
> >   #define VUART_PFN_OFFSET 3
> > +#define IOREQ_SERVER_PFN_OFFSET 4
> > +
> > +#define NR_IOREQ_SERVER_PAGES 8
> > +#define NR_MAGIC_PAGES (4 + NR_IOREQ_SERVER_PAGES)
> > +
> > +#define GUEST_MAGIC_BASE_PFN (GUEST_MAGIC_BASE >> XC_PAGE_SHIFT)
> > +
> > +#define special_pfn(x)  (GUEST_MAGIC_BASE_PFN + (x))
> Why introduce 'magic pages' for Arm? It's quite a horrible hack that we have 
> begun to do away with by adding resource mapping.
This would require us to mandate at least Linux 4.17 in a domain that 
will run an IOREQ server. If we don't mandate this, the minimum version 
would be 4.10 where DM OP was introduced.
Because of XSA-300, we could technically not safely run an IOREQ server 
with existing Linux. So it is probably OK to enforce the use of the 
acquire interface.
Note that I haven't yet looked at the rest of the series. So I am not 
sure if there is more work necessary to enable it.
Cheers,

--
Julien Grall