Re: [PATCH 1/6] mm: kfence: simplify kfence pool initialization

[Marco Elver <elver@google.com>]

On Tue, 28 Mar 2023 at 11:58, Muchun Song <songmuchun@bytedance.com> wrote:
>
> There are three similar loops to initialize kfence pool, we could merge
> all of them into one loop to simplify the code and make code more
> efficient.
>
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>

Reviewed-by: Marco Elver <elver@google.com>

> ---
>  mm/kfence/core.c | 47 ++++++-----------------------------------------
>  1 file changed, 6 insertions(+), 41 deletions(-)
>
> diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> index 7d01a2c76e80..de62a84d4830 100644
> --- a/mm/kfence/core.c
> +++ b/mm/kfence/core.c
> @@ -539,35 +539,10 @@ static void rcu_guarded_free(struct rcu_head *h)
>  static unsigned long kfence_init_pool(void)
>  {
>         unsigned long addr = (unsigned long)__kfence_pool;
> -       struct page *pages;
>         int i;
>
>         if (!arch_kfence_init_pool())
>                 return addr;
> -
> -       pages = virt_to_page(__kfence_pool);
> -
> -       /*
> -        * Set up object pages: they must have PG_slab set, to avoid freeing
> -        * these as real pages.
> -        *
> -        * We also want to avoid inserting kfence_free() in the kfree()
> -        * fast-path in SLUB, and therefore need to ensure kfree() correctly
> -        * enters __slab_free() slow-path.
> -        */
> -       for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) {
> -               struct slab *slab = page_slab(nth_page(pages, i));
> -
> -               if (!i || (i % 2))
> -                       continue;
> -
> -               __folio_set_slab(slab_folio(slab));
> -#ifdef CONFIG_MEMCG
> -               slab->memcg_data = (unsigned long)&kfence_metadata[i / 2 - 1].objcg |
> -                                  MEMCG_DATA_OBJCGS;
> -#endif
> -       }
> -
>         /*
>          * Protect the first 2 pages. The first page is mostly unnecessary, and
>          * merely serves as an extended guard page. However, adding one
> @@ -581,8 +556,9 @@ static unsigned long kfence_init_pool(void)
>                 addr += PAGE_SIZE;
>         }
>
> -       for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++) {
> +       for (i = 0; i < CONFIG_KFENCE_NUM_OBJECTS; i++, addr += 2 * PAGE_SIZE) {
>                 struct kfence_metadata *meta = &kfence_metadata[i];
> +               struct slab *slab = page_slab(virt_to_page(addr));
>
>                 /* Initialize metadata. */
>                 INIT_LIST_HEAD(&meta->list);
> @@ -593,26 +569,15 @@ static unsigned long kfence_init_pool(void)
>
>                 /* Protect the right redzone. */
>                 if (unlikely(!kfence_protect(addr + PAGE_SIZE)))
> -                       goto reset_slab;
> -
> -               addr += 2 * PAGE_SIZE;
> -       }
> -
> -       return 0;
> -
> -reset_slab:
> -       for (i = 0; i < KFENCE_POOL_SIZE / PAGE_SIZE; i++) {
> -               struct slab *slab = page_slab(nth_page(pages, i));
> +                       return addr;
>
> -               if (!i || (i % 2))
> -                       continue;
> +               __folio_set_slab(slab_folio(slab));
>  #ifdef CONFIG_MEMCG
> -               slab->memcg_data = 0;
> +               slab->memcg_data = (unsigned long)&meta->objcg | MEMCG_DATA_OBJCGS;
>  #endif
> -               __folio_clear_slab(slab_folio(slab));
>         }
>
> -       return addr;
> +       return 0;
>  }
>
>  static bool __init kfence_init_pool_early(void)
> --
> 2.11.0
>