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    Subject[PATCH v4 12/19] mm: pagewalk: Add test_p?d callbacks
    Date
    It is useful to be able to skip parts of the page table tree even when
    walking without VMAs. Add test_p?d callbacks similar to test_walk but
    which are called just before a table at that level is walked. If the
    callback returns non-zero then the entire table is skipped.

    Signed-off-by: Steven Price <steven.price@arm.com>
    ---
    include/linux/mm.h | 11 +++++++++++
    mm/pagewalk.c | 24 ++++++++++++++++++++++++
    2 files changed, 35 insertions(+)

    diff --git a/include/linux/mm.h b/include/linux/mm.h
    index 1a4b1615d012..4755af1779f6 100644
    --- a/include/linux/mm.h
    +++ b/include/linux/mm.h
    @@ -1427,6 +1427,11 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma,
    * value means "do page table walk over the current vma,"
    * and a negative one means "abort current page table walk
    * right now." 1 means "skip the current vma."
    + * @test_pmd: similar to test_walk(), but called for every pmd.
    + * @test_pud: similar to test_walk(), but called for every pud.
    + * @test_p4d: similar to test_walk(), but called for every p4d.
    + * Returning 0 means walk this part of the page tables,
    + * returning 1 means to skip this range.
    * @mm: mm_struct representing the target process of page table walk
    * @vma: vma currently walked (NULL if walking outside vmas)
    * @private: private data for callbacks' usage
    @@ -1451,6 +1456,12 @@ struct mm_walk {
    struct mm_walk *walk);
    int (*test_walk)(unsigned long addr, unsigned long next,
    struct mm_walk *walk);
    + int (*test_pmd)(unsigned long addr, unsigned long next,
    + pmd_t *pmd_start, struct mm_walk *walk);
    + int (*test_pud)(unsigned long addr, unsigned long next,
    + pud_t *pud_start, struct mm_walk *walk);
    + int (*test_p4d)(unsigned long addr, unsigned long next,
    + p4d_t *p4d_start, struct mm_walk *walk);
    struct mm_struct *mm;
    struct vm_area_struct *vma;
    void *private;
    diff --git a/mm/pagewalk.c b/mm/pagewalk.c
    index dac0c848b458..231655db1295 100644
    --- a/mm/pagewalk.c
    +++ b/mm/pagewalk.c
    @@ -32,6 +32,14 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
    unsigned long next;
    int err = 0;

    + if (walk->test_pmd) {
    + err = walk->test_pmd(addr, end, pmd_offset(pud, 0), walk);
    + if (err < 0)
    + return err;
    + if (err > 0)
    + return 0;
    + }
    +
    pmd = pmd_offset(pud, addr);
    do {
    again:
    @@ -82,6 +90,14 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
    unsigned long next;
    int err = 0;

    + if (walk->test_pud) {
    + err = walk->test_pud(addr, end, pud_offset(p4d, 0), walk);
    + if (err < 0)
    + return err;
    + if (err > 0)
    + return 0;
    + }
    +
    pud = pud_offset(p4d, addr);
    do {
    again:
    @@ -124,6 +140,14 @@ static int walk_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,
    unsigned long next;
    int err = 0;

    + if (walk->test_p4d) {
    + err = walk->test_p4d(addr, end, p4d_offset(pgd, 0), walk);
    + if (err < 0)
    + return err;
    + if (err > 0)
    + return 0;
    + }
    +
    p4d = p4d_offset(pgd, addr);
    do {
    next = p4d_addr_end(addr, end);
    --
    2.20.1
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