[PATCH 3/3] x86: implement HAVE_PMD_SPECAIL

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>

We can use the same bit as for special PTE.

There's no conflict with _PAGE_SPLITTING since it's only defined for PSE
pmd, but special PMD is only valid for non-PSE.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 arch/x86/Kconfig               |    1 +
 arch/x86/include/asm/pgtable.h |   14 +++++++++++++-
 2 files changed, 14 insertions(+), 1 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 50a1d1f..b2146c3 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -97,6 +97,7 @@ config X86
 	select KTIME_SCALAR if X86_32
 	select GENERIC_STRNCPY_FROM_USER
 	select GENERIC_STRNLEN_USER
+	select HAVE_PMD_SPECIAL
 
 config INSTRUCTION_DECODER
 	def_bool (KPROBES || PERF_EVENTS || UPROBES)
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 49afb3f..ff61694 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -167,6 +167,12 @@ static inline int has_transparent_hugepage(void)
 }
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
+static inline int pmd_special(pmd_t pmd)
+{
+	return !pmd_trans_huge(pmd) &&
+		pmd_flags(pmd) & _PAGE_SPECIAL;
+}
+
 static inline pte_t pte_set_flags(pte_t pte, pteval_t set)
 {
 	pteval_t v = native_pte_val(pte);
@@ -290,6 +296,11 @@ static inline pmd_t pmd_mknotpresent(pmd_t pmd)
 	return pmd_clear_flags(pmd, _PAGE_PRESENT);
 }
 
+static inline pmd_t pmd_mkspecial(pmd_t pmd)
+{
+	return pmd_set_flags(pmd, _PAGE_SPECIAL);
+}
+
 /*
  * Mask out unsupported bits in a present pgprot.  Non-present pgprots
  * can use those bits for other purposes, so leave them be.
@@ -474,7 +485,8 @@ static inline pte_t *pte_offset_kernel(pmd_t *pmd, unsigned long address)
 
 static inline int pmd_bad(pmd_t pmd)
 {
-	return (pmd_flags(pmd) & ~_PAGE_USER) != _KERNPG_TABLE;
+	pmdval_t flags = pmd_flags(pmd);
+	return (flags & ~(_PAGE_USER | _PAGE_SPECIAL)) != _KERNPG_TABLE;
 }
 
 static inline unsigned long pages_to_mb(unsigned long npg)
-- 
1.7.7.6

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