[PATCH v1 2/3] io_uring/rsrc: don't rely on user vaddr alignment

[Pavel Begunkov <asml.silence@gmail.com>]

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 <david@redhat.com>
Fixes: a8edbb424b139 ("io_uring/rsrc: enable multi-hugepage buffer coalescing")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 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;
 
 	/*
 	 * 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;
 };
 
 bool io_rsrc_cache_init(struct io_ring_ctx *ctx);
-- 
2.49.0