Re: [Xen-devel] [PATCH v02 6/7] arm: introduce do_translate_pagetable hypercall

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2014-07-04 at 15:05 +0100, Stefano Stabellini wrote:
> > diff --git a/xen/include/public/xen.h b/xen/include/public/xen.h
> > index 8c5697e..91ca6a1 100644
> > --- a/xen/include/public/xen.h
> > +++ b/xen/include/public/xen.h
> > @@ -101,6 +101,7 @@ DEFINE_XEN_GUEST_HANDLE(xen_ulong_t);
> >  #define __HYPERVISOR_kexec_op             37
> >  #define __HYPERVISOR_tmem_op              38
> >  #define __HYPERVISOR_xc_reserved_op       39 /* reserved for XenClient */
> > +#define __HYPERVISOR_translate_pagetable  40
> 
> It might be best to introduce this hypercall as an arch memory op
> (xen/arch/arm/mm.c:arch_memory_op), rather than a full blown new
> hypercall.

Or physdev op perhaps?

>  Otherwise you'll need to provide an empty stub implementation
> for x86.

All unused hypercalls -ENOSYS automatically without stubs I think.

Are there any security concerns with exposing machine addresses to
guests? There are certainly "breaking the abstraction" concerns, but
that's unavoidable here I think.

> >  /* Architecture-specific hypercall definitions. */
> >  #define __HYPERVISOR_arch_0               48
> > diff --git a/xen/include/xen/hypercall.h b/xen/include/xen/hypercall.h
> > index a9e5229..a025435 100644
> > --- a/xen/include/xen/hypercall.h
> > +++ b/xen/include/xen/hypercall.h
> > @@ -136,6 +136,18 @@ extern long
> >  do_tmem_op(
> >      XEN_GUEST_HANDLE_PARAM(tmem_op_t) uops);
> >  
> > +struct xen_pagetable_addr {
> > +   u32 reg;
> > +   u32 paddr;
> > +   u32 maddr;
> 
> Could you please comment what these fields are for exactly?

And mark them as IN/OUT as appropriate please.

Also the physical and machine addresses should always be 64 bits for
compatibility with future larger chips.

Having done that you then need padding after reg or to reorder things to
avoid holes on 64-bit. Or maybe reg should be 64-bit, depends what it
is. Either way the 32-bit and 64-bit layout of this struct should be
identical.

Ian.



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