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    SubjectRe: [PATCH v2 4/7] ARM: mm: print out correct page table entries
    On Wed, Jun 02, 2021 at 03:02:43PM +0800, Kefeng Wang wrote:
    > Like commit 67ce16ec15ce ("arm64: mm: print out correct page table entries")
    > does, drop the struct mm_struct argument of show_pte(), print the tables
    > based on the faulting address.
    >
    > Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>

    This can be misleading on 32-bit ARM.

    The effective page tables for each thread are the threads *own* page
    tables. There is no hardware magic for addresses above PAGE_OFFSET being
    directed to the init_mm page tables.

    So, when we hit a fault in kernel space, we need to be printing the
    currently in-use page tables associated with the running thread.

    Hence:

    > /*
    > - * This is useful to dump out the page tables associated with
    > - * 'addr' in mm 'mm'.
    > + * Dump out the page tables associated with 'addr' in the currently active mm
    > */
    > -void show_pte(const char *lvl, struct mm_struct *mm, unsigned long addr)
    > +void show_pte(const char *lvl, unsigned long addr)
    > {
    > pgd_t *pgd;
    > -
    > - if (!mm)
    > + struct mm_struct *mm;
    > +
    > + if (addr < TASK_SIZE) {
    > + mm = current->active_mm;
    > + if (mm == &init_mm) {
    > + printk("%s[%08lx] user address but active_mm is swapper\n",
    > + lvl, addr);
    > + return;
    > + }
    > + } else {
    > mm = &init_mm;
    > + }

    is incorrect here.

    It's completely fine for architectures where kernel accesses always go
    to the init_mm page tables, but for 32-bit ARM that is not the case.

    --
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