On 2/17/25 19:38, Ryan Roberts wrote:
> A call to vmalloc_huge() may cause memory blocks to be mapped at pmd or
> pud level. But it is possible to subsequently call vunmap_range() on a
> sub-range of the mapped memory, which partially overlaps a pmd or pud.
> In this case, vmalloc unmaps the entire pmd or pud so that the
> no-overlapping portion is also unmapped. Clearly that would have a bad
> outcome, but it's not something that any callers do today as far as I
> can tell. So I guess it's just expected that callers will not do this.
>
> However, it would be useful to know if this happened in future; let's
> add a warning to cover the eventuality.
>
> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
LGTM and stands on its own independent of the series here.
Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> ---
> mm/vmalloc.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 61981ee1c9d2..a7e34e6936d2 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -374,8 +374,10 @@ static void vunmap_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
> if (cleared || pmd_bad(*pmd))
> *mask |= PGTBL_PMD_MODIFIED;
>
> - if (cleared)
> + if (cleared) {
> + WARN_ON(next - addr < PMD_SIZE);
> continue;
> + }
> if (pmd_none_or_clear_bad(pmd))
> continue;
> vunmap_pte_range(pmd, addr, next, mask);
> @@ -399,8 +401,10 @@ static void vunmap_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
> if (cleared || pud_bad(*pud))
> *mask |= PGTBL_PUD_MODIFIED;
>
> - if (cleared)
> + if (cleared) {
> + WARN_ON(next - addr < PUD_SIZE);
> continue;
> + }
> if (pud_none_or_clear_bad(pud))
> continue;
> vunmap_pmd_range(pud, addr, next, mask);
