[PATCH -V2 20/26] powerpc/THP: Differentiate THP PMD entries from HUGETLB PMD entries

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>

HUGETLB clear the top bit of PMD entries and use that to indicate
a HUGETLB page directory. Since we store pfns in PMDs for THP,
we would have the top bit cleared by default. Add the top bit mask
for THP PMD entries and clear that when we are looking for pmd_pfn.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/pgtable.h |   15 ++++++++++++---
 arch/powerpc/mm/pgtable.c          |    5 ++++-
 arch/powerpc/mm/pgtable_64.c       |    2 +-
 3 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
index e637842..09f3a77 100644
--- a/arch/powerpc/include/asm/pgtable.h
+++ b/arch/powerpc/include/asm/pgtable.h
@@ -31,7 +31,7 @@ struct mm_struct;
 #define PMD_HUGE_EXEC		0x004 /* No execute on POWER4 and newer (we invert) */
 #define PMD_HUGE_SPLITTING	0x008
 #define PMD_HUGE_HASHPTE	0x010
-#define PMD_ISHUGE		0x020
+#define _PMD_ISHUGE		0x020
 #define PMD_HUGE_DIRTY		0x080 /* C: page changed */
 #define PMD_HUGE_ACCESSED	0x100 /* R: page referenced */
 #define PMD_HUGE_RW		0x200 /* software: user write access allowed */
@@ -44,6 +44,14 @@ struct mm_struct;
 #define PMD_HUGE_RPN_SHIFT	PTE_RPN_SHIFT
 #define HUGE_PAGE_SIZE		(ASM_CONST(1) << 24)
 #define HUGE_PAGE_MASK		(~(HUGE_PAGE_SIZE - 1))
+/*
+ * HugeTLB looks at the top bit of the Linux page table entries to
+ * decide whether it is a huge page directory or not. Mark HUGE
+ * PMD to differentiate
+ */
+#define PMD_HUGE_NOT_HUGETLB	(ASM_CONST(1) << 63)
+#define PMD_ISHUGE		(_PMD_ISHUGE | PMD_HUGE_NOT_HUGETLB)
+#define PMD_HUGE_PROTBITS	(0xfff | PMD_HUGE_NOT_HUGETLB)
 
 #ifndef __ASSEMBLY__
 extern void hpte_need_hugepage_flush(struct mm_struct *mm, unsigned long addr,
@@ -61,7 +69,8 @@ static inline unsigned long pmd_pfn(pmd_t pmd)
 	/*
 	 * Only called for huge page pmd
 	 */
-	return pmd_val(pmd) >> PMD_HUGE_RPN_SHIFT;
+	unsigned long val = pmd_val(pmd) & ~PMD_HUGE_PROTBITS;
+	return val  >> PMD_HUGE_RPN_SHIFT;
 }
 
 static inline int pmd_young(pmd_t pmd)
@@ -95,7 +104,7 @@ static inline int pmd_trans_splitting(pmd_t pmd)
 
 static inline int pmd_trans_huge(pmd_t pmd)
 {
-	return pmd_val(pmd) & PMD_ISHUGE;
+	return ((pmd_val(pmd) & PMD_ISHUGE) ==  PMD_ISHUGE);
 }
 
 /* We will enable it in the last patch */
diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
index 77ce864..84e7b71 100644
--- a/arch/powerpc/mm/pgtable.c
+++ b/arch/powerpc/mm/pgtable.c
@@ -524,7 +524,10 @@ static pmd_t pmd_set_protbits(pmd_t pmd, pgprot_t pgprot)
 pmd_t pfn_pmd(unsigned long pfn, pgprot_t pgprot)
 {
 	pmd_t pmd;
-
+	/*
+	 * We cannot support that many PFNs
+	 */
+	VM_BUG_ON(pfn & PMD_HUGE_NOT_HUGETLB);
 	pmd_val(pmd) = pfn << PMD_HUGE_RPN_SHIFT;
 	pmd_val(pmd) |= PMD_ISHUGE;
 	pmd = pmd_set_protbits(pmd, pgprot);
diff --git a/arch/powerpc/mm/pgtable_64.c b/arch/powerpc/mm/pgtable_64.c
index 313fe01..a506059 100644
--- a/arch/powerpc/mm/pgtable_64.c
+++ b/arch/powerpc/mm/pgtable_64.c
@@ -345,7 +345,7 @@ EXPORT_SYMBOL(__iounmap_at);
 struct page *pmd_page(pmd_t pmd)
 {
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	if (pmd_val(pmd) & PMD_ISHUGE)
+	if ((pmd_val(pmd) & PMD_ISHUGE) == PMD_ISHUGE)
 		return pfn_to_page(pmd_pfn(pmd));
 #endif
 	return virt_to_page(pmd_page_vaddr(pmd));
-- 
1.7.10