On 2/5/25 20:39, Ryan Roberts wrote:
> Commit f7ee1f13d606 ("mm/vmalloc: enable mapping of huge pages at pte
> level in vmap") added its support by reusing the set_huge_pte_at() API,
> which is otherwise only used for user mappings. But when unmapping those
> huge ptes, it continued to call ptep_get_and_clear(), which is a
> layering violation. To date, the only arch to implement this support is
> powerpc and it all happens to work ok for it.
>
> But arm64's implementation of ptep_get_and_clear() can not be safely
> used to clear a previous set_huge_pte_at(). So let's introduce a new
> arch opt-in function, arch_vmap_pte_range_unmap_size(), which can
> provide the size of a (present) pte. Then we can call
> huge_ptep_get_and_clear() to tear it down properly.
>
> Note that if vunmap_range() is called with a range that starts in the
> middle of a huge pte-mapped page, we must unmap the entire huge page so
> the behaviour is consistent with pmd and pud block mappings. In this
> case emit a warning just like we do for pmd/pud mappings.
>
> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
> ---
> include/linux/vmalloc.h | 8 ++++++++
> mm/vmalloc.c | 18 ++++++++++++++++--
> 2 files changed, 24 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> index 31e9ffd936e3..16dd4cba64f2 100644
> --- a/include/linux/vmalloc.h
> +++ b/include/linux/vmalloc.h
> @@ -113,6 +113,14 @@ static inline unsigned long arch_vmap_pte_range_map_size(unsigned long addr, uns
> }
> #endif
>
> +#ifndef arch_vmap_pte_range_unmap_size
> +static inline unsigned long arch_vmap_pte_range_unmap_size(unsigned long addr,
> + pte_t *ptep)
> +{
> + return PAGE_SIZE;
> +}
> +#endif
> +
> #ifndef arch_vmap_pte_supported_shift
> static inline int arch_vmap_pte_supported_shift(unsigned long size)
> {
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index fcdf67d5177a..6111ce900ec4 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -350,12 +350,26 @@ static void vunmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
> pgtbl_mod_mask *mask)
> {
> pte_t *pte;
> + pte_t ptent;
> + unsigned long size = PAGE_SIZE;
Default fallback size being PAGE_SIZE like before.
>
> pte = pte_offset_kernel(pmd, addr);
> do {
> - pte_t ptent = ptep_get_and_clear(&init_mm, addr, pte);
> +#ifdef CONFIG_HUGETLB_PAGE
> + size = arch_vmap_pte_range_unmap_size(addr, pte);
> + if (size != PAGE_SIZE) {
> + if (WARN_ON(!IS_ALIGNED(addr, size))) {
> + addr = ALIGN_DOWN(addr, size);
> + pte = PTR_ALIGN_DOWN(pte, sizeof(*pte) * (size >> PAGE_SHIFT));
> + }
> + ptent = huge_ptep_get_and_clear(&init_mm, addr, pte, size);
> + if (WARN_ON(end - addr < size))
> + size = end - addr;
> + } else
> +#endif
> + ptent = ptep_get_and_clear(&init_mm, addr, pte);
ptep_get_and_clear() gets used both, when !HUGETLB_PAGE or HUGETLB_PAGE with
arch_vmap_pte_range_unmap_size() returned value being PAGE_SIZE, which makes
sense.
> WARN_ON(!pte_none(ptent) && !pte_present(ptent));
> - } while (pte++, addr += PAGE_SIZE, addr != end);
> + } while (pte += (size >> PAGE_SHIFT), addr += size, addr != end);
> *mask |= PGTBL_PTE_MODIFIED;
> }
>
LGTM
Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
