"Aneesh Kumar K.V" [off-list ref] writes:

Paul Mackerras [off-list ref] writes:

quoted

 #define _PAGE_PTE		(1ul << 62)	/* distinguishes PTEs from pointers */
 #define _PAGE_PRESENT		(1ul << 63)	/* pte contains a translation */

diff --git a/arch/powerpc/mm/pgtable-book3s64.c b/arch/powerpc/mm/pgtable-book3s64.c
index f4f437c..7ff0289 100644
--- a/arch/powerpc/mm/pgtable-book3s64.c
+++ b/arch/powerpc/mm/pgtable-book3s64.c

@@ -86,7 +86,7 @@ pmd_t pfn_pmd(unsigned long pfn, pgprot_t pgprot)
 {
 	unsigned long pmdv;

-	pmdv = (pfn << PAGE_SHIFT) & PTE_RPN_MASK;
+	pmdv = ((pfn << PAGE_SHIFT) & PTE_RPN_MASK) | _PAGE_LARGE;
 	return pmd_set_protbits(__pmd(pmdv), pgprot);
 }

I will look at this and see if can make the patch simpler. But do we
really want to use the pte bit for this ? Aren't we low on free pte bits

Ok this will work, provided we are ok to take up two pte bits for this
So we can use make_huge_pte() to fixup the pte entry for hugetlb and
pmd_mkhuge() to fixup the THP.

Now the question will be how will we support _PAGE_DEVMAP (for nvidmm).
We don't have free software pte bits after we make the above change.

NOTE: We do have 3 reserved bits(ppc bit 4-6 ) can we use that ?

-aneesh