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