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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 24.06.25 14:20, Pavel Begunkov wrote: > On 6/24/25 12:53, David Hildenbrand wrote: >> On 24.06.25 12:35, Pavel Begunkov wrote: >>> There is no guaranteed alignment for user pointers, however the >>> calculation of an offset of the first page into a folio after >>> coalescing uses some weird bit mask logic, get rid of it. >>> >>> Cc: stable@vger.kernel.org >>> Reported-by: David Hildenbrand >>> Fixes: a8edbb424b139 ("io_uring/rsrc: enable multi-hugepage buffer coalescing") >>> Signed-off-by: Pavel Begunkov >>> --- >>>   io_uring/rsrc.c | 8 +++++++- >>>   io_uring/rsrc.h | 1 + >>>   2 files changed, 8 insertions(+), 1 deletion(-) >>> >>> diff --git a/io_uring/rsrc.c b/io_uring/rsrc.c >>> index e83a294c718b..5132f8df600f 100644 >>> --- a/io_uring/rsrc.c >>> +++ b/io_uring/rsrc.c >>> @@ -734,6 +734,8 @@ bool io_check_coalesce_buffer(struct page **page_array, int nr_pages, >>>       data->nr_pages_mid = folio_nr_pages(folio); >>>       data->folio_shift = folio_shift(folio); >>> +    data->first_page_offset = page_array[0] - compound_head(page_array[0]); >>> +    data->first_page_offset <<= PAGE_SHIFT; >> >> Would that also cover when we have something like >> >> nr_pages = 4 >> pages[0] = folio_page(folio, 1); >> pages[1] = folio_page(folio, 2); >> pages[2] = folio_page(folio2, 1); >> pages[3] = folio_page(folio2, 2); >> >> Note that we can create all kinds of crazy partially-mapped THP layouts using VMAs. > > It'll see that pages[2] is not the first page of folio2 > and return that it can't be coalesced > > if (/* ... */ || folio_page_idx(folio, page_array[i]) != 0) > return false; Ah okay, that makes sense. It might be clearer at some point to coalesce folio ranges (e.g., folio,idx,len) instead, representing them in a different temporary structure. -- Cheers, David / dhildenb