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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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]); Note: pointer arithmetic on "struct page" does not work reliably for very large folios (eg., 1 GiB hugetlb) in all configs (!CONFIG_SPARSEMEM_VMEMMAP) I assume this can be data->first_page_offset = folio_page_idx(folio, page_array[0]); > + data->first_page_offset <<= PAGE_SHIFT; > > /* > * Check if pages are contiguous inside a folio, and all folios have > @@ -830,7 +832,11 @@ static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx, > if (coalesced) > imu->folio_shift = data.folio_shift; > refcount_set(&imu->refs, 1); > - off = (unsigned long) iov->iov_base & ((1UL << imu->folio_shift) - 1); > + > + off = (unsigned long)iov->iov_base & ~PAGE_MASK; > + if (coalesced) > + off += data.first_page_offset; > + > node->buf = imu; > ret = 0; > > diff --git a/io_uring/rsrc.h b/io_uring/rsrc.h > index 0d2138f16322..d823554a8817 100644 > --- a/io_uring/rsrc.h > +++ b/io_uring/rsrc.h > @@ -49,6 +49,7 @@ struct io_imu_folio_data { > unsigned int nr_pages_mid; > unsigned int folio_shift; > unsigned int nr_folios; > + unsigned long first_page_offset; Heh, is it actually "first_folio_offset" ? Alternatively, call it "first_folio_page_idx" or sth like that and leave the shift to the user. -- Cheers, David / dhildenb