[Xen-devel] Re: [PATCH 2/2] Linux support for hugepages as a Xen PVguest

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>>> Dave McCracken <dcm@xxxxxxxx> 10.10.08 17:06 >>>
>> > --- linux-2.6.18-xen//./mm/hugetlb.c 2008-07-17 09:54:19.000000000 -0500
>> > +++ linux-hpage/./mm/hugetlb.c 2008-10-02 15:07:54.000000000 -0500
>> > @@ -294,12 +294,14 @@ static pte_t make_huge_pte(struct vm_are
>> > int writable)
>> >  {
>> > pte_t entry;
>> > + pgprot_t pgprot;
>> >
>> > + pgprot = __pgprot(pgprot_val(vma->vm_page_prot) | _PAGE_PRESENT);
>> > if (writable) {
>> > entry =
>> > -      pte_mkwrite(pte_mkdirty(mk_pte(page, vma->vm_page_prot)));
>> > +      pte_mkwrite(pte_mkdirty(mk_pte(page, pgprot)));
>> > } else {
>> > -  entry = pte_wrprotect(mk_pte(page, vma->vm_page_prot));
>> > +  entry = pte_wrprotect(mk_pte(page, pgprot));
>> > }
>> > entry = pte_mkyoung(entry);
>> > entry = pte_mkhuge(entry);
>>
>> Why do we need to do something different for Xen here?
>
>In the original implementation _PAGE_PRESENT is set in later macros.  Xen 
>needs it early to trigger the proper phys_to_machine() translation.

That should then better be taken care of in the place where _PAGE_PRESENT
gets actually set. Also, doesn't vma->vm_page_prot already properly
reflect the intended setting of _PAGE_PRESENT?

Jan


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