Re: [Xen-devel] x86-64 machine_to_phys vs NX bit

[John Byrne <john.l.byrne@xxxxxx>]

Keir Fraser wrote:
> On 13/11/06 8:07 am, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:
>
> > > There was a bug in my previous patch. (There's nothing like trying to
> > > get to sleep and realizing you've screwed up.) The x86 pae
> > > PHYSICAL_PAGE_MASK I defined was incorrect because PAGE_MASK was only a
> > > long. I hope I haven't done anything else wrong.
> > I don't think this is correct - machine_to_phys() translates a machine address
> > to a physical one, and in that translation the upper bits matter only as much
> > as mfn_to_pfn() should return an invalid indicator if any of them is set. In
> > turn,
> > it should be the caller's responsibility to make sure the NX bit (and any
> > potential
> > other one being set beyond bit 52) gets masked off *before* calling this
> > function. (Specifically, the preserving of the lower bits is to properly
> > translate
> > a non-page aligned address, not to preserve attribute bits read from a page
> > table entry).
> Yes, we should keep the old machine_to_phys() definition and rename John's
> new version as pte_machine_to_phys(). The latter should be used in all
> contexts where machine_to_phys() currently operates on a pte (that's most of
> its uses, actually). This is a worthwhile cleanup and clarification. Could
> you respin the patch, John?
>
>  Thanks,
>  Keir
I've  made the change. I'll send it out after I've built and tested it.

John


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