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

[Jeremy Fitzhardinge <jeremy@goop.org>]

From: Dave McCracken <dave.mccracken@oracle.com>

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.

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..4cfd4de 100644
--- a/arch/x86/include/asm/hugetlb.h
+++ b/arch/x86/include/asm/hugetlb.h
@@ -36,16 +36,24 @@ 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);
+	set_pmd((pmd_t *)ptep, __pmd(pte_val(pte)));
 }
 
 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 +74,25 @@ 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)