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    Subject[PATCH v15 13/23] 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.

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

    diff --git a/include/linux/pagewalk.h b/include/linux/pagewalk.h
    index ed2bb399fac2..fe61448c5900 100644
    --- a/include/linux/pagewalk.h
    +++ b/include/linux/pagewalk.h
    @@ -24,6 +24,11 @@ struct mm_walk;
    * "do page table walk over the current vma", returning
    * a negative value means "abort current page table walk
    * right now" and returning 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.
    *
    * p?d_entry callbacks are called even if those levels are folded on a
    * particular architecture/configuration.
    @@ -46,6 +51,12 @@ struct mm_walk_ops {
    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);
    };

    /**
    diff --git a/mm/pagewalk.c b/mm/pagewalk.c
    index 626e7fdb0508..4616281f5b69 100644
    --- a/mm/pagewalk.c
    +++ b/mm/pagewalk.c
    @@ -34,6 +34,14 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
    const struct mm_walk_ops *ops = walk->ops;
    int err = 0;

    + if (ops->test_pmd) {
    + err = ops->test_pmd(addr, end, pmd_offset(pud, 0UL), walk);
    + if (err < 0)
    + return err;
    + if (err > 0)
    + return 0;
    + }
    +
    pmd = pmd_offset(pud, addr);
    do {
    again:
    @@ -85,6 +93,14 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
    const struct mm_walk_ops *ops = walk->ops;
    int err = 0;

    + if (ops->test_pud) {
    + err = ops->test_pud(addr, end, pud_offset(p4d, 0UL), walk);
    + if (err < 0)
    + return err;
    + if (err > 0)
    + return 0;
    + }
    +
    pud = pud_offset(p4d, addr);
    do {
    again:
    @@ -128,6 +144,14 @@ static int walk_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,
    const struct mm_walk_ops *ops = walk->ops;
    int err = 0;

    + if (ops->test_p4d) {
    + err = ops->test_p4d(addr, end, p4d_offset(pgd, 0UL), 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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