Re: [PATCH v2 2/2] mm: use aligned address in copy_user_gigantic_page()

David Hildenbrand
2024-10-28T10:01:53Z

On 26.10.24 07:43, Kefeng Wang wrote:
> When copying gigantic page, it copies page from the first page to the
> last page, if directly passing addr_hint which maybe not the address
> of the first page of folio, then some archs could flush the wrong cache
> if it does use the addr_hint as a hint. For non-gigantic page, it
> calculates the base address inside, even passed the wrong addr_hint, it
> only has performance impact as the process_huge_page() wants to process
> target page last to keep its cache lines hot), no functional impact.
>
> Let's pass the real accessed address to copy_user_large_folio() and use
> the aligned address in copy_user_gigantic_page() to fix it.
>
> Fixes: 530dd9926dc1 ("mm: memory: improve copy_user_large_folio()")
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
> v2:
> - update changelog to clarify the impact, per Andrew
>
> mm/hugetlb.c | 5 ++---
> mm/memory.c | 1 +
> 2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 2c8c5da0f5d3..15b5d46d49d2 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5338,7 +5338,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
> break;
> }
> ret = copy_user_large_folio(new_folio, pte_folio,
> - ALIGN_DOWN(addr, sz), dst_vma);
> + addr, dst_vma);
> folio_put(pte_folio);
> if (ret) {
> folio_put(new_folio);
> @@ -6641,8 +6641,7 @@ int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
> *foliop = NULL;
> goto out;
> }
> - ret = copy_user_large_folio(folio, *foliop,
> - ALIGN_DOWN(dst_addr, size), dst_vma);
> + ret = copy_user_large_folio(folio, *foliop, dst_addr, dst_vma);
> folio_put(*foliop);
> *foliop = NULL;
> if (ret) {
> diff --git a/mm/memory.c b/mm/memory.c
> index ef47b7ea5ddd..e5284bab659d 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -6860,6 +6860,7 @@ static int copy_user_gigantic_page(struct folio *dst, struct folio *src,
> struct page *dst_page;
> struct page *src_page;
>
> + addr = ALIGN_DOWN(addr, folio_size(dst));

Same thing, please make it clearer that there is an "addr_hint" and an
"addr".

--
Cheers,

David / dhildenb