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    Subject[PATCH v4 2/4] arm64: mm: don't call page table ctors for init_mm
    From
    init_mm doesn't require page table lock to be initialized at
    any level. Add a separate page table allocator for it, and the
    new one skips page table ctors.

    The ctors allocate memory when ALLOC_SPLIT_PTLOCKS is set. Not
    calling them avoids memory leak in case we call pte_free_kernel()
    on init_mm.

    Acked-by: Mark Rutland <mark.rutland@arm.com>
    Signed-off-by: Yu Zhao <yuzhao@google.com>
    ---
    arch/arm64/mm/mmu.c | 15 +++++++++++++--
    1 file changed, 13 insertions(+), 2 deletions(-)

    diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
    index f704b291f2c5..d1dc2a2777aa 100644
    --- a/arch/arm64/mm/mmu.c
    +++ b/arch/arm64/mm/mmu.c
    @@ -370,6 +370,16 @@ static void __create_pgd_mapping(pgd_t *pgdir, phys_addr_t phys,
    } while (pgdp++, addr = next, addr != end);
    }

    +static phys_addr_t pgd_kernel_pgtable_alloc(int shift)
    +{
    + void *ptr = (void *)__get_free_page(PGALLOC_GFP);
    + BUG_ON(!ptr);
    +
    + /* Ensure the zeroed page is visible to the page table walker */
    + dsb(ishst);
    + return __pa(ptr);
    +}
    +
    static phys_addr_t pgd_pgtable_alloc(int shift)
    {
    void *ptr = (void *)__get_free_page(PGALLOC_GFP);
    @@ -594,7 +604,7 @@ static int __init map_entry_trampoline(void)
    /* Map only the text into the trampoline page table */
    memset(tramp_pg_dir, 0, PGD_SIZE);
    __create_pgd_mapping(tramp_pg_dir, pa_start, TRAMP_VALIAS, PAGE_SIZE,
    - prot, pgd_pgtable_alloc, 0);
    + prot, pgd_kernel_pgtable_alloc, 0);

    /* Map both the text and data into the kernel page table */
    __set_fixmap(FIX_ENTRY_TRAMP_TEXT, pa_start, prot);
    @@ -1070,7 +1080,8 @@ int arch_add_memory(int nid, u64 start, u64 size, struct vmem_altmap *altmap,
    flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;

    __create_pgd_mapping(swapper_pg_dir, start, __phys_to_virt(start),
    - size, PAGE_KERNEL, pgd_pgtable_alloc, flags);
    + size, PAGE_KERNEL, pgd_kernel_pgtable_alloc,
    + flags);

    return __add_pages(nid, start >> PAGE_SHIFT, size >> PAGE_SHIFT,
    altmap, want_memblock);
    --
    2.21.0.360.g471c308f928-goog
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