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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 4 Aug 2020, Julien Grall wrote:
> 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.

+1