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    Subject[PATCH 09/10] mm/hmm: allow to mirror vma of a file on a DAX backed filesystem
    Date
    From: Jérôme Glisse <jglisse@redhat.com>

    This add support to mirror vma which is an mmap of a file which is on
    a filesystem that using a DAX block device. There is no reason not to
    support that case.

    Note that unlike GUP code we do not take page reference hence when we
    back-off we have nothing to undo.

    Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Dan Williams <dan.j.williams@intel.com>
    Cc: Ralph Campbell <rcampbell@nvidia.com>
    Cc: John Hubbard <jhubbard@nvidia.com>
    ---
    mm/hmm.c | 133 ++++++++++++++++++++++++++++++++++++++++++++++---------
    1 file changed, 112 insertions(+), 21 deletions(-)

    diff --git a/mm/hmm.c b/mm/hmm.c
    index 8b87e1813313..1a444885404e 100644
    --- a/mm/hmm.c
    +++ b/mm/hmm.c
    @@ -334,6 +334,7 @@ EXPORT_SYMBOL(hmm_mirror_unregister);

    struct hmm_vma_walk {
    struct hmm_range *range;
    + struct dev_pagemap *pgmap;
    unsigned long last;
    bool fault;
    bool block;
    @@ -508,6 +509,15 @@ static inline uint64_t pmd_to_hmm_pfn_flags(struct hmm_range *range, pmd_t pmd)
    range->flags[HMM_PFN_VALID];
    }

    +static inline uint64_t pud_to_hmm_pfn_flags(struct hmm_range *range, pud_t pud)
    +{
    + if (!pud_present(pud))
    + return 0;
    + return pud_write(pud) ? range->flags[HMM_PFN_VALID] |
    + range->flags[HMM_PFN_WRITE] :
    + range->flags[HMM_PFN_VALID];
    +}
    +
    static int hmm_vma_handle_pmd(struct mm_walk *walk,
    unsigned long addr,
    unsigned long end,
    @@ -529,8 +539,19 @@ static int hmm_vma_handle_pmd(struct mm_walk *walk,
    return hmm_vma_walk_hole_(addr, end, fault, write_fault, walk);

    pfn = pmd_pfn(pmd) + pte_index(addr);
    - for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++)
    + for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++) {
    + if (pmd_devmap(pmd)) {
    + hmm_vma_walk->pgmap = get_dev_pagemap(pfn,
    + hmm_vma_walk->pgmap);
    + if (unlikely(!hmm_vma_walk->pgmap))
    + return -EBUSY;
    + }
    pfns[i] = hmm_pfn_from_pfn(range, pfn) | cpu_flags;
    + }
    + if (hmm_vma_walk->pgmap) {
    + put_dev_pagemap(hmm_vma_walk->pgmap);
    + hmm_vma_walk->pgmap = NULL;
    + }
    hmm_vma_walk->last = end;
    return 0;
    }
    @@ -617,10 +638,24 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
    if (fault || write_fault)
    goto fault;

    + if (pte_devmap(pte)) {
    + hmm_vma_walk->pgmap = get_dev_pagemap(pte_pfn(pte),
    + hmm_vma_walk->pgmap);
    + if (unlikely(!hmm_vma_walk->pgmap))
    + return -EBUSY;
    + } else if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL) && pte_special(pte)) {
    + *pfn = range->values[HMM_PFN_SPECIAL];
    + return -EFAULT;
    + }
    +
    *pfn = hmm_pfn_from_pfn(range, pte_pfn(pte)) | cpu_flags;
    return 0;

    fault:
    + if (hmm_vma_walk->pgmap) {
    + put_dev_pagemap(hmm_vma_walk->pgmap);
    + hmm_vma_walk->pgmap = NULL;
    + }
    pte_unmap(ptep);
    /* Fault any virtual address we were asked to fault */
    return hmm_vma_walk_hole_(addr, end, fault, write_fault, walk);
    @@ -708,12 +743,84 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp,
    return r;
    }
    }
    + if (hmm_vma_walk->pgmap) {
    + put_dev_pagemap(hmm_vma_walk->pgmap);
    + hmm_vma_walk->pgmap = NULL;
    + }
    pte_unmap(ptep - 1);

    hmm_vma_walk->last = addr;
    return 0;
    }

    +static int hmm_vma_walk_pud(pud_t *pudp,
    + unsigned long start,
    + unsigned long end,
    + struct mm_walk *walk)
    +{
    + struct hmm_vma_walk *hmm_vma_walk = walk->private;
    + struct hmm_range *range = hmm_vma_walk->range;
    + struct vm_area_struct *vma = walk->vma;
    + unsigned long addr = start, next;
    + pmd_t *pmdp;
    + pud_t pud;
    + int ret;
    +
    +again:
    + pud = READ_ONCE(*pudp);
    + if (pud_none(pud))
    + return hmm_vma_walk_hole(start, end, walk);
    +
    + if (pud_huge(pud) && pud_devmap(pud)) {
    + unsigned long i, npages, pfn;
    + uint64_t *pfns, cpu_flags;
    + bool fault, write_fault;
    +
    + if (!pud_present(pud))
    + return hmm_vma_walk_hole(start, end, walk);
    +
    + i = (addr - range->start) >> PAGE_SHIFT;
    + npages = (end - addr) >> PAGE_SHIFT;
    + pfns = &range->pfns[i];
    +
    + cpu_flags = pud_to_hmm_pfn_flags(range, pud);
    + hmm_range_need_fault(hmm_vma_walk, pfns, npages,
    + cpu_flags, &fault, &write_fault);
    + if (fault || write_fault)
    + return hmm_vma_walk_hole_(addr, end, fault,
    + write_fault, walk);
    +
    + pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
    + for (i = 0; i < npages; ++i, ++pfn) {
    + hmm_vma_walk->pgmap = get_dev_pagemap(pfn,
    + hmm_vma_walk->pgmap);
    + if (unlikely(!hmm_vma_walk->pgmap))
    + return -EBUSY;
    + pfns[i] = hmm_pfn_from_pfn(range, pfn) | cpu_flags;
    + }
    + if (hmm_vma_walk->pgmap) {
    + put_dev_pagemap(hmm_vma_walk->pgmap);
    + hmm_vma_walk->pgmap = NULL;
    + }
    + hmm_vma_walk->last = end;
    + return 0;
    + }
    +
    + split_huge_pud(vma, pudp, addr);
    + if (pud_none(*pudp))
    + goto again;
    +
    + pmdp = pmd_offset(pudp, addr);
    + do {
    + next = pmd_addr_end(addr, end);
    + ret = hmm_vma_walk_pmd(pmdp, addr, next, walk);
    + if (ret)
    + return ret;
    + } while (pmdp++, addr = next, addr != end);
    +
    + return 0;
    +}
    +
    static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask,
    unsigned long start, unsigned long end,
    struct mm_walk *walk)
    @@ -786,14 +893,6 @@ static void hmm_pfns_clear(struct hmm_range *range,
    *pfns = range->values[HMM_PFN_NONE];
    }

    -static void hmm_pfns_special(struct hmm_range *range)
    -{
    - unsigned long addr = range->start, i = 0;
    -
    - for (; addr < range->end; addr += PAGE_SIZE, i++)
    - range->pfns[i] = range->values[HMM_PFN_SPECIAL];
    -}
    -
    /*
    * hmm_range_register() - start tracking change to CPU page table over a range
    * @range: range
    @@ -911,12 +1010,6 @@ long hmm_range_snapshot(struct hmm_range *range)
    if (vma == NULL || (vma->vm_flags & device_vma))
    return -EFAULT;

    - /* FIXME support dax */
    - if (vma_is_dax(vma)) {
    - hmm_pfns_special(range);
    - return -EINVAL;
    - }
    -
    if (is_vm_hugetlb_page(vma)) {
    struct hstate *h = hstate_vma(vma);

    @@ -940,6 +1033,7 @@ long hmm_range_snapshot(struct hmm_range *range)
    }

    range->vma = vma;
    + hmm_vma_walk.pgmap = NULL;
    hmm_vma_walk.last = start;
    hmm_vma_walk.fault = false;
    hmm_vma_walk.range = range;
    @@ -951,6 +1045,7 @@ long hmm_range_snapshot(struct hmm_range *range)
    mm_walk.pte_entry = NULL;
    mm_walk.test_walk = NULL;
    mm_walk.hugetlb_entry = NULL;
    + mm_walk.pud_entry = hmm_vma_walk_pud;
    mm_walk.pmd_entry = hmm_vma_walk_pmd;
    mm_walk.pte_hole = hmm_vma_walk_hole;
    mm_walk.hugetlb_entry = hmm_vma_walk_hugetlb_entry;
    @@ -1018,12 +1113,6 @@ long hmm_range_fault(struct hmm_range *range, bool block)
    if (vma == NULL || (vma->vm_flags & device_vma))
    return -EFAULT;

    - /* FIXME support dax */
    - if (vma_is_dax(vma)) {
    - hmm_pfns_special(range);
    - return -EINVAL;
    - }
    -
    if (is_vm_hugetlb_page(vma)) {
    struct hstate *h = hstate_vma(vma);

    @@ -1047,6 +1136,7 @@ long hmm_range_fault(struct hmm_range *range, bool block)
    }

    range->vma = vma;
    + hmm_vma_walk.pgmap = NULL;
    hmm_vma_walk.last = start;
    hmm_vma_walk.fault = true;
    hmm_vma_walk.block = block;
    @@ -1059,6 +1149,7 @@ long hmm_range_fault(struct hmm_range *range, bool block)
    mm_walk.pte_entry = NULL;
    mm_walk.test_walk = NULL;
    mm_walk.hugetlb_entry = NULL;
    + mm_walk.pud_entry = hmm_vma_walk_pud;
    mm_walk.pmd_entry = hmm_vma_walk_pmd;
    mm_walk.pte_hole = hmm_vma_walk_hole;
    mm_walk.hugetlb_entry = hmm_vma_walk_hugetlb_entry;
    --
    2.17.2
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