Re: [Xen-devel] [PATCH v2 1/2] x86: add p2m_mmio_write_dm

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
> Sent: Monday, August 25, 2014 3:46 AM
> 
> >>> On 22.08.14 at 21:18, <wei.ye@xxxxxxxxx> wrote:
> > --- a/xen/arch/x86/mm/p2m-ept.c
> > +++ b/xen/arch/x86/mm/p2m-ept.c
> > @@ -127,6 +127,7 @@ static void ept_p2m_type_to_flags(ept_entry_t
> *entry, p2m_type_t type, p2m_acces
> >          case p2m_ram_logdirty:
> >          case p2m_ram_ro:
> >          case p2m_ram_shared:
> > +        case p2m_mmio_write_dm:
> >              entry->r = entry->x = 1;
> >              entry->w = 0;
> >              break;
> 
> Is that really what you want? I.e. should such pages be executable?
> 
> > --- a/xen/arch/x86/mm/p2m-pt.c
> > +++ b/xen/arch/x86/mm/p2m-pt.c
> > @@ -98,6 +98,7 @@ static unsigned long p2m_type_to_flags(p2m_type_t t,
> mfn_t mfn)
> >      case p2m_ram_ro:
> >      case p2m_ram_logdirty:
> >      case p2m_ram_shared:
> > +    case p2m_mmio_write_dm:
> >          return flags | P2M_BASE_FLAGS;
> 
> Same here - this would likely better be grouped with
> p2m_grant_map_ro.
> 
> > --- a/xen/include/asm-x86/p2m.h
> > +++ b/xen/include/asm-x86/p2m.h
> > @@ -71,6 +71,7 @@ typedef enum {
> >      p2m_ram_shared = 12,          /* Shared or sharable memory */
> >      p2m_ram_broken = 13,          /* Broken page, access cause
> domain crash */
> >      p2m_map_foreign  = 14,        /* ram pages from foreign
> domain */
> > +    p2m_mmio_write_dm = 15,       /* Read-only; write go to the
> device model */
> >  } p2m_type_t;
> 
> I'm still not really convinced introducing a new p2m type is the right
> approach here, but I'll leave the final decision to Tim.
> 

From previous discussion Tim is OK with either approach, i.e. either adding
a new p2m type for plain read-only mapping, or treating it as a plain
mmio_dm. Given adding such a new type is straightforward, we want to
pursue new p2m type to implement real write-protection behavior.

Tim please correct me if you see other issues.

Thanks
Kevin

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