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From: Jeremy Fitzhardinge on 20 Jul 2010 16:00
From: Dave McCracken <dave.mccracken(a)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(a)oracle.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge(a)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)


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Prev: trace-cmd: Fix a couple of crashes.
Next: [PATCH] cfq: improve fsync performance for small files