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SubjectRe: [PATCH v9 19/21] mm: Add generic ptdump
On Mon, Jul 22, 2019 at 04:42:08PM +0100, Steven Price wrote:
> Add a generic version of page table dumping that architectures can
> opt-in to
>
> Signed-off-by: Steven Price <steven.price@arm.com>

[...]

> +#ifdef CONFIG_KASAN
> +/*
> + * This is an optimization for KASAN=y case. Since all kasan page tables
> + * eventually point to the kasan_early_shadow_page we could call note_page()
> + * right away without walking through lower level page tables. This saves
> + * us dozens of seconds (minutes for 5-level config) while checking for
> + * W+X mapping or reading kernel_page_tables debugfs file.
> + */
> +static inline bool kasan_page_table(struct ptdump_state *st, void *pt,
> + unsigned long addr)
> +{
> + if (__pa(pt) == __pa(kasan_early_shadow_pmd) ||
> +#ifdef CONFIG_X86
> + (pgtable_l5_enabled() &&
> + __pa(pt) == __pa(kasan_early_shadow_p4d)) ||
> +#endif
> + __pa(pt) == __pa(kasan_early_shadow_pud)) {
> + st->note_page(st, addr, 5, pte_val(kasan_early_shadow_pte[0]));
> + return true;
> + }
> + return false;

Having you tried this with CONFIG_DEBUG_VIRTUAL?

The kasan_early_shadow_pmd is a kernel object rather than a linear map
object, so you should use __pa_symbol for that.

It's a bit horrid to have to test multiple levels in one function; can't
we check the relevant level inline in each of the test_p?d funcs?

They're optional anyway, so they only need to be defined for
CONFIG_KASAN.

Thanks,
Mark.

> +}
> +#else
> +static inline bool kasan_page_table(struct ptdump_state *st, void *pt,
> + unsigned long addr)
> +{
> + return false;
> +}
> +#endif
> +
> +static int ptdump_test_p4d(unsigned long addr, unsigned long next,
> + p4d_t *p4d, struct mm_walk *walk)
> +{
> + struct ptdump_state *st = walk->private;
> +
> + if (kasan_page_table(st, p4d, addr))
> + return 1;
> + return 0;
> +}
> +static int ptdump_test_pud(unsigned long addr, unsigned long next,
> + pud_t *pud, struct mm_walk *walk)
> +{
> + struct ptdump_state *st = walk->private;
> +
> + if (kasan_page_table(st, pud, addr))
> + return 1;
> + return 0;
> +}
> +
> +static int ptdump_test_pmd(unsigned long addr, unsigned long next,
> + pmd_t *pmd, struct mm_walk *walk)
> +{
> + struct ptdump_state *st = walk->private;
> +
> + if (kasan_page_table(st, pmd, addr))
> + return 1;
> + return 0;
> +}
> +
> +static int ptdump_hole(unsigned long addr, unsigned long next,
> + struct mm_walk *walk)
> +{
> + struct ptdump_state *st = walk->private;
> +
> + st->note_page(st, addr, -1, 0);
> +
> + return 0;
> +}
> +
> +void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm)
> +{
> + struct mm_walk walk = {
> + .mm = mm,
> + .pgd_entry = ptdump_pgd_entry,
> + .p4d_entry = ptdump_p4d_entry,
> + .pud_entry = ptdump_pud_entry,
> + .pmd_entry = ptdump_pmd_entry,
> + .pte_entry = ptdump_pte_entry,
> + .test_p4d = ptdump_test_p4d,
> + .test_pud = ptdump_test_pud,
> + .test_pmd = ptdump_test_pmd,
> + .pte_hole = ptdump_hole,
> + .private = st
> + };
> + const struct ptdump_range *range = st->range;
> +
> + down_read(&mm->mmap_sem);
> + while (range->start != range->end) {
> + walk_page_range(range->start, range->end, &walk);
> + range++;
> + }
> + up_read(&mm->mmap_sem);
> +
> + /* Flush out the last page */
> + st->note_page(st, 0, 0, 0);
> +}
> --
> 2.20.1
>

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