Re: [PATCH -V5 19/25] powerpc/THP: Differentiate THP PMD entries from HUGETLB PMD entries

Michael Ellerman [off-list ref] writes:

On Thu, Apr 04, 2013 at 11:27:57AM +0530, Aneesh Kumar K.V wrote:

quoted

From: "Aneesh Kumar K.V" <redacted>

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.

@@ -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,

@@ -84,7 +93,8 @@ static inline unsigned long pmd_pfn(pmd_t pmd)
 	/*
 	 * Only called for hugepage pmd
 	 */
-	return pmd_val(pmd) >> PMD_HUGE_RPN_SHIFT;
+	unsigned long val = pmd_val(pmd) & ~PMD_HUGE_PROTBITS;
+	return val  >> PMD_HUGE_RPN_SHIFT;
 }

This is breaking the 32-bit build for me (pmac32_defconfig):

arch/powerpc/include/asm/pgtable.h:123:2: error: left shift count >= width of type [-Werror]

diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
index 5617dee..30c765a 100644
--- a/arch/powerpc/include/asm/pgtable.h
+++ b/arch/powerpc/include/asm/pgtable.h

@@ -110,11 +110,6 @@ static inline int has_transparent_hugepage(void)
 	return 1;
 }
 
-#else
-#define pmd_large(pmd)		0
-#define has_transparent_hugepage() 0
-#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
-
 static inline unsigned long pmd_pfn(pmd_t pmd)
 {
 	/*

@@ -124,6 +119,11 @@ static inline unsigned long pmd_pfn(pmd_t pmd)
 	return val  >> PMD_HUGE_RPN_SHIFT;
 }
 
+#else
+#define pmd_large(pmd)		0
+#define has_transparent_hugepage() 0
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+
 static inline int pmd_young(pmd_t pmd)
 {
 	return pmd_val(pmd) & PMD_HUGE_ACCESSED;