Re: [syzbot] KMSAN: uninit-value in follow_page_pte

[syzbot <syzbot+2aee6839a252e612ce34@syzkaller.appspotmail.com>]

> #syz test

This crash does not have a reproducer. I cannot test it.

>
> This is a test patch to fix the KMSAN uninit-value in follow_page_pte.
>
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5189,6 +5189,10 @@ unsigned long alloc_pages_bulk_noprof(gfp_t gfp, 
> int preferred_nid,
>
>                  prep_new_page(page, 0, gfp, 0);
>                  set_page_refcounted(page);
> +
> +               trace_mm_page_alloc(page, 0, gfp, ac.migratetype);
> +               kmsan_alloc_page(page, 0, gfp);
> +
>                  page_array[nr_populated++] = page;
>          }
>
> @@ -6911,6 +6915,12 @@ static void split_free_frozen_pages(struct 
> list_head *list, gfp_t gfp_mask)
>                          int i;
>
>                          post_alloc_hook(page, order, gfp_mask);
> +                       /*
> +                        * Initialize KMSAN state right after 
> post_alloc_hook().
> +                        * This prepares the pages for subsequent outer 
> callers
> +                        * that might free sub-pages after the split.
> +                        */
> +                       kmsan_alloc_page(page, order, gfp_mask);
>                          if (!order)
>                                  continue;
>
> @@ -7117,6 +7127,8 @@ int alloc_contig_frozen_range_noprof(unsigned long 
> start, unsigned long end,
>
>                  check_new_pages(head, order);
>                  prep_new_page(head, order, gfp_mask, 0);
> +
> +               kmsan_alloc_page(head, order, gfp_mask);
>          } else {
>                  ret = -EINVAL;
>                  WARN(true, "PFN range: requested [%lu, %lu), allocated 
> [%lu, %lu)\n",
>