[PATCH] x86/hugetlb: use set_pmd for huge pte operations

[Jeremy Fitzhardinge <jeremy@goop.org>]

On x86, a huge pte is logically a pte, but structurally a pmd.  Among
other issues, pmds and ptes overload some flags for multiple uses (PAT
vs PSE), so it is necessary to know which structural level a pagetable
entry is in order interpret it properly.

When huge pages are used within a paravirtualized system, it is therefore
appropriate to use the pmd set of function to operate on them, so that
the hypervisor can correctly validate the update.

[ Add fix for 32-bit non-PAE with two-level pagetable - Jeremy ]

Signed-off-by: Dave McCracken<dave.mccracken@oracle.com>
Signed-off-by: Jeremy Fitzhardinge<jeremy.fitzhardinge@citrix.com>

diff --git a/arch/x86/include/asm/hugetlb.h b/arch/x86/include/asm/hugetlb.h
index 439a9ac..bf88684 100644
--- a/arch/x86/include/asm/hugetlb.h
+++ b/arch/x86/include/asm/hugetlb.h
@@ -36,16 +36,28 @@ static inline void hugetlb_free_pgd_range(struct mmu_gather *tlb,
  	free_pgd_range(tlb, addr, end, floor, ceiling);
  }

+static inline pte_t huge_ptep_get(pte_t *ptep)
+{
+	return *ptep;
+}
+
  static inline void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
  				   pte_t *ptep, pte_t pte)
  {
-	set_pte_at(mm, addr, ptep, pte);
+#if PAGETABLE_LEVELS>= 3
+	set_pmd((pmd_t *)ptep, native_make_pmd(native_pte_val(pte)));
+#else
+	set_pgd((pgd_t *)ptep, native_make_pgd(native_pte_val(pte)));
+#endif
  }

  static inline pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
  					    unsigned long addr, pte_t *ptep)
  {
-	return ptep_get_and_clear(mm, addr, ptep);
+	pte_t pte = huge_ptep_get(ptep);
+
+	set_huge_pte_at(mm, addr, ptep, __pte(0));
+	return pte;
  }

  static inline void huge_ptep_clear_flush(struct vm_area_struct *vma,
@@ -66,19 +78,25 @@ static inline pte_t huge_pte_wrprotect(pte_t pte)
  static inline void huge_ptep_set_wrprotect(struct mm_struct *mm,
  					   unsigned long addr, pte_t *ptep)
  {
-	ptep_set_wrprotect(mm, addr, ptep);
+	pte_t pte = huge_ptep_get(ptep);
+
+	pte = pte_wrprotect(pte);
+	set_huge_pte_at(mm, addr, ptep, pte);
  }

  static inline int huge_ptep_set_access_flags(struct vm_area_struct *vma,
  					     unsigned long addr, pte_t *ptep,
  					     pte_t pte, int dirty)
  {
-	return ptep_set_access_flags(vma, addr, ptep, pte, dirty);
-}
+	pte_t oldpte = huge_ptep_get(ptep);
+	int changed = !pte_same(oldpte, pte);

-static inline pte_t huge_ptep_get(pte_t *ptep)
-{
-	return *ptep;
+	if (changed&&  dirty) {
+		set_huge_pte_at(vma->vm_mm, addr, ptep, pte);
+		flush_tlb_page(vma, addr);
+	}
+
+	return changed;
  }

  static inline int arch_prepare_hugepage(struct page *page)