From: Bobby Eshleman bobbyeshleman@meta.com
get_sg_table() emitted one PAGE_SIZE sg entry per page even when the underlying folio was larger.
Instead, walk folios[] and emit one sg entry per folio. When folios represent large pages (as is for MFD_HUGETLB), each sg entry is a large page. Normal PAGE_SIZE sg tables are unchanged.
This is helpful for importers like net/core/devmem that expect dmabuf sg entries to be size and length aligned. Prior to this patch udmabuf handed over one PAGE_SIZE sg entry per page, so devmem only saw PAGE_SIZE chunks regardless of the underlying folio size.
dma_map_sgtable() does not always merge contiguous pages for us, so we do this internally before exporting.
Signed-off-by: Bobby Eshleman bobbyeshleman@meta.com --- drivers/dma-buf/udmabuf.c | 52 ++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 47 insertions(+), 5 deletions(-)
diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c index 94b8ecb892bb..9b751dd98b12 100644 --- a/drivers/dma-buf/udmabuf.c +++ b/drivers/dma-buf/udmabuf.c @@ -141,26 +141,68 @@ static void vunmap_udmabuf(struct dma_buf *buf, struct iosys_map *map) vm_unmap_ram(map->vaddr, ubuf->pagecount); }
+/* Return the number of contiguous pages backed by the folio at @i. + * A udmabuf may map only part of a folio, or reference the same folio + * in multiple non-contiguous runs, so folio_nr_pages() can't be used. + */ +static pgoff_t udmabuf_folio_nr_pages(struct udmabuf *ubuf, pgoff_t i) +{ + struct folio *f = ubuf->folios[i]; + pgoff_t j; + + for (j = 1; i + j < ubuf->pagecount; j++) { + if (ubuf->folios[i + j] != f) + break; + /* Same folio, but not a sequential offset within it. */ + if (ubuf->offsets[i + j] != ubuf->offsets[i] + j * PAGE_SIZE) + break; + } + return j; +} + +/* Count the contiguous folio runs in @ubuf, one sg entry per run. + * + * Coalescing folios into a single sg entry up front lets importers actually + * see large chunks. We can't rely on dma_map_sgtable() to do this for us as + * the dma_map_direct() path preserves the input scatterlist lengths verbatim. + */ +static unsigned int udmabuf_sg_nents(struct udmabuf *ubuf) +{ + unsigned int nents = 0; + pgoff_t i; + + for (i = 0; i < ubuf->pagecount; i += udmabuf_folio_nr_pages(ubuf, i)) + nents++; + return nents; +} + static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf, enum dma_data_direction direction) { struct udmabuf *ubuf = buf->priv; - struct sg_table *sg; struct scatterlist *sgl; - unsigned int i = 0; + struct sg_table *sg; + pgoff_t i, run; + unsigned int nents; int ret;
+ nents = udmabuf_sg_nents(ubuf); + sg = kzalloc_obj(*sg); if (!sg) return ERR_PTR(-ENOMEM);
- ret = sg_alloc_table(sg, ubuf->pagecount, GFP_KERNEL); + ret = sg_alloc_table(sg, nents, GFP_KERNEL); if (ret < 0) goto err_alloc;
- for_each_sg(sg->sgl, sgl, ubuf->pagecount, i) - sg_set_folio(sgl, ubuf->folios[i], PAGE_SIZE, + sgl = sg->sgl; + for (i = 0; i < ubuf->pagecount; i += run) { + run = udmabuf_folio_nr_pages(ubuf, i); + sg_set_folio(sgl, ubuf->folios[i], run << PAGE_SHIFT, ubuf->offsets[i]); + sgl = sg_next(sgl); + }
ret = dma_map_sgtable(dev, sg, direction, 0); if (ret < 0)