forked from luck/tmp_suning_uos_patched
[PATCH] Hugetlb: Copy on Write support
Implement copy-on-write support for hugetlb mappings so MAP_PRIVATE can be supported. This helps us to safely use hugetlb pages in many more applications. The patch makes the following changes. If needed, I also have it broken out according to the following paragraphs. 1. Add a pair of functions to set/clear write access on huge ptes. The writable check in make_huge_pte is moved out to the caller for use by COW later. 2. Hugetlb copy-on-write requires special case handling in the following situations: - copy_hugetlb_page_range() - Copied pages must be write protected so a COW fault will be triggered (if necessary) if those pages are written to. - find_or_alloc_huge_page() - Only MAP_SHARED pages are added to the page cache. MAP_PRIVATE pages still need to be locked however. 3. Provide hugetlb_cow() and calls from hugetlb_fault() and hugetlb_no_page() which handles the COW fault by making the actual copy. 4. Remove the check in hugetlbfs_file_map() so that MAP_PRIVATE mmaps will be allowed. Make MAP_HUGETLB exempt from the depricated VM_RESERVED mapping check. Signed-off-by: David Gibson <david@gibson.dropbear.id.au> Signed-off-by: Adam Litke <agl@us.ibm.com> Cc: William Lee Irwin III <wli@holomorphy.com> Cc: "Seth, Rohit" <rohit.seth@intel.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
parent
86e5216f8d
commit
1e8f889b10
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@ -100,9 +100,6 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
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loff_t len, vma_len;
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int ret;
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if ((vma->vm_flags & (VM_MAYSHARE | VM_WRITE)) == VM_WRITE)
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return -EINVAL;
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if (vma->vm_pgoff & (HPAGE_SIZE / PAGE_SIZE - 1))
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return -EINVAL;
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127
mm/hugetlb.c
127
mm/hugetlb.c
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@ -261,11 +261,12 @@ struct vm_operations_struct hugetlb_vm_ops = {
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.nopage = hugetlb_nopage,
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};
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static pte_t make_huge_pte(struct vm_area_struct *vma, struct page *page)
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static pte_t make_huge_pte(struct vm_area_struct *vma, struct page *page,
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int writable)
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{
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pte_t entry;
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if (vma->vm_flags & VM_WRITE) {
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if (writable) {
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entry =
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pte_mkwrite(pte_mkdirty(mk_pte(page, vma->vm_page_prot)));
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} else {
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@ -277,12 +278,27 @@ static pte_t make_huge_pte(struct vm_area_struct *vma, struct page *page)
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return entry;
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}
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static void set_huge_ptep_writable(struct vm_area_struct *vma,
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unsigned long address, pte_t *ptep)
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{
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pte_t entry;
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entry = pte_mkwrite(pte_mkdirty(*ptep));
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ptep_set_access_flags(vma, address, ptep, entry, 1);
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update_mmu_cache(vma, address, entry);
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lazy_mmu_prot_update(entry);
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}
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int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
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struct vm_area_struct *vma)
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{
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pte_t *src_pte, *dst_pte, entry;
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struct page *ptepage;
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unsigned long addr;
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int cow;
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cow = (vma->vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
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for (addr = vma->vm_start; addr < vma->vm_end; addr += HPAGE_SIZE) {
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src_pte = huge_pte_offset(src, addr);
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@ -294,6 +310,8 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
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spin_lock(&dst->page_table_lock);
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spin_lock(&src->page_table_lock);
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if (!pte_none(*src_pte)) {
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if (cow)
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ptep_set_wrprotect(src, addr, src_pte);
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entry = *src_pte;
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ptepage = pte_page(entry);
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get_page(ptepage);
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@ -346,7 +364,7 @@ void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
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}
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static struct page *find_or_alloc_huge_page(struct address_space *mapping,
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unsigned long idx)
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unsigned long idx, int shared)
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{
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struct page *page;
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int err;
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@ -364,26 +382,80 @@ static struct page *find_or_alloc_huge_page(struct address_space *mapping,
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goto out;
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}
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err = add_to_page_cache(page, mapping, idx, GFP_KERNEL);
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if (err) {
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put_page(page);
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hugetlb_put_quota(mapping);
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if (err == -EEXIST)
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goto retry;
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page = NULL;
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if (shared) {
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err = add_to_page_cache(page, mapping, idx, GFP_KERNEL);
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if (err) {
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put_page(page);
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hugetlb_put_quota(mapping);
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if (err == -EEXIST)
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goto retry;
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page = NULL;
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}
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} else {
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/* Caller expects a locked page */
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lock_page(page);
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}
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out:
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return page;
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}
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static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,
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unsigned long address, pte_t *ptep, pte_t pte)
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{
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struct page *old_page, *new_page;
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int i, avoidcopy;
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old_page = pte_page(pte);
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/* If no-one else is actually using this page, avoid the copy
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* and just make the page writable */
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avoidcopy = (page_count(old_page) == 1);
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if (avoidcopy) {
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set_huge_ptep_writable(vma, address, ptep);
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return VM_FAULT_MINOR;
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}
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page_cache_get(old_page);
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new_page = alloc_huge_page();
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if (!new_page) {
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page_cache_release(old_page);
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/* Logically this is OOM, not a SIGBUS, but an OOM
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* could cause the kernel to go killing other
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* processes which won't help the hugepage situation
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* at all (?) */
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return VM_FAULT_SIGBUS;
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}
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spin_unlock(&mm->page_table_lock);
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for (i = 0; i < HPAGE_SIZE/PAGE_SIZE; i++)
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copy_user_highpage(new_page + i, old_page + i,
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address + i*PAGE_SIZE);
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spin_lock(&mm->page_table_lock);
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ptep = huge_pte_offset(mm, address & HPAGE_MASK);
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if (likely(pte_same(*ptep, pte))) {
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/* Break COW */
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set_huge_pte_at(mm, address, ptep,
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make_huge_pte(vma, new_page, 1));
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/* Make the old page be freed below */
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new_page = old_page;
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}
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page_cache_release(new_page);
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page_cache_release(old_page);
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return VM_FAULT_MINOR;
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}
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int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
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unsigned long address, pte_t *ptep)
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unsigned long address, pte_t *ptep, int write_access)
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{
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int ret = VM_FAULT_SIGBUS;
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unsigned long idx;
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unsigned long size;
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struct page *page;
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struct address_space *mapping;
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pte_t new_pte;
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mapping = vma->vm_file->f_mapping;
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idx = ((address - vma->vm_start) >> HPAGE_SHIFT)
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@ -393,10 +465,13 @@ int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
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* Use page lock to guard against racing truncation
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* before we get page_table_lock.
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*/
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page = find_or_alloc_huge_page(mapping, idx);
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page = find_or_alloc_huge_page(mapping, idx,
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vma->vm_flags & VM_SHARED);
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if (!page)
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goto out;
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BUG_ON(!PageLocked(page));
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spin_lock(&mm->page_table_lock);
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size = i_size_read(mapping->host) >> HPAGE_SHIFT;
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if (idx >= size)
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@ -407,7 +482,15 @@ int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
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goto backout;
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add_mm_counter(mm, file_rss, HPAGE_SIZE / PAGE_SIZE);
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set_huge_pte_at(mm, address, ptep, make_huge_pte(vma, page));
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new_pte = make_huge_pte(vma, page, ((vma->vm_flags & VM_WRITE)
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&& (vma->vm_flags & VM_SHARED)));
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set_huge_pte_at(mm, address, ptep, new_pte);
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if (write_access && !(vma->vm_flags & VM_SHARED)) {
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/* Optimization, do the COW without a second fault */
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ret = hugetlb_cow(mm, vma, address, ptep, new_pte);
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}
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spin_unlock(&mm->page_table_lock);
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unlock_page(page);
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out:
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@ -426,6 +509,7 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
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{
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pte_t *ptep;
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pte_t entry;
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int ret;
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ptep = huge_pte_alloc(mm, address);
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if (!ptep)
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@ -433,13 +517,18 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
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entry = *ptep;
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if (pte_none(entry))
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return hugetlb_no_page(mm, vma, address, ptep);
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return hugetlb_no_page(mm, vma, address, ptep, write_access);
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/*
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* We could get here if another thread instantiated the pte
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* before the test above.
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*/
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return VM_FAULT_MINOR;
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ret = VM_FAULT_MINOR;
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spin_lock(&mm->page_table_lock);
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/* Check for a racing update before calling hugetlb_cow */
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if (likely(pte_same(entry, *ptep)))
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if (write_access && !pte_write(entry))
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ret = hugetlb_cow(mm, vma, address, ptep, entry);
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spin_unlock(&mm->page_table_lock);
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return ret;
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}
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int follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
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