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    Subject[PATCHv2, RFC 28/30] thp: handle write-protect exception to file-backed huge pages
    Date
    From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>

    Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    ---
    mm/huge_memory.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
    1 file changed, 67 insertions(+), 2 deletions(-)

    diff --git a/mm/huge_memory.c b/mm/huge_memory.c
    index d1adaea..a416a77 100644
    --- a/mm/huge_memory.c
    +++ b/mm/huge_memory.c
    @@ -1339,7 +1339,6 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
    unsigned long mmun_start; /* For mmu_notifiers */
    unsigned long mmun_end; /* For mmu_notifiers */

    - VM_BUG_ON(!vma->anon_vma);
    haddr = address & HPAGE_PMD_MASK;
    if (is_huge_zero_pmd(orig_pmd))
    goto alloc;
    @@ -1349,7 +1348,7 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,

    page = pmd_page(orig_pmd);
    VM_BUG_ON(!PageCompound(page) || !PageHead(page));
    - if (page_mapcount(page) == 1) {
    + if (PageAnon(page) && page_mapcount(page) == 1) {
    pmd_t entry;
    entry = pmd_mkyoung(orig_pmd);
    entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
    @@ -1357,10 +1356,72 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
    update_mmu_cache_pmd(vma, address, pmd);
    ret |= VM_FAULT_WRITE;
    goto out_unlock;
    + } else if ((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
    + (VM_WRITE|VM_SHARED)) {
    + struct vm_fault vmf;
    + pmd_t entry;
    + struct address_space *mapping;
    +
    + /* not yet impemented */
    + VM_BUG_ON(!vma->vm_ops || !vma->vm_ops->page_mkwrite);
    +
    + vmf.virtual_address = (void __user *)haddr;
    + vmf.pgoff = page->index;
    + vmf.flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
    + vmf.page = page;
    +
    + page_cache_get(page);
    + spin_unlock(&mm->page_table_lock);
    +
    + ret = vma->vm_ops->page_mkwrite(vma, &vmf);
    + if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE))) {
    + page_cache_release(page);
    + goto out;
    + }
    + if (unlikely(!(ret & VM_FAULT_LOCKED))) {
    + lock_page(page);
    + if (!page->mapping) {
    + ret = 0; /* retry */
    + unlock_page(page);
    + page_cache_release(page);
    + goto out;
    + }
    + } else
    + VM_BUG_ON(!PageLocked(page));
    + spin_lock(&mm->page_table_lock);
    + if (unlikely(!pmd_same(*pmd, orig_pmd))) {
    + unlock_page(page);
    + page_cache_release(page);
    + goto out_unlock;
    + }
    +
    + flush_cache_page(vma, address, pmd_pfn(orig_pmd));
    + entry = pmd_mkyoung(orig_pmd);
    + entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
    + if (pmdp_set_access_flags(vma, haddr, pmd, entry, 1))
    + update_mmu_cache_pmd(vma, address, pmd);
    + ret = VM_FAULT_WRITE;
    + spin_unlock(&mm->page_table_lock);
    +
    + mapping = page->mapping;
    + set_page_dirty(page);
    + unlock_page(page);
    + page_cache_release(page);
    + if (mapping) {
    + /*
    + * Some device drivers do not set page.mapping
    + * but still dirty their pages
    + */
    + balance_dirty_pages_ratelimited(mapping);
    + }
    + return ret;
    }
    get_page(page);
    spin_unlock(&mm->page_table_lock);
    alloc:
    + if (unlikely(anon_vma_prepare(vma)))
    + return VM_FAULT_OOM;
    +
    if (transparent_hugepage_enabled(vma) &&
    !transparent_hugepage_debug_cow())
    new_page = alloc_hugepage_vma(transparent_hugepage_defrag(vma),
    @@ -1424,6 +1485,10 @@ alloc:
    add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
    put_huge_zero_page();
    } else {
    + if (!PageAnon(page)) {
    + add_mm_counter(mm, MM_FILEPAGES, -HPAGE_PMD_NR);
    + add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR);
    + }
    VM_BUG_ON(!PageHead(page));
    page_remove_rmap(page);
    put_page(page);
    --
    1.7.10.4


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