On 6/4/26 02:42, Bobby Eshleman wrote:
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.
Required by net/core/devmem to support rx-buf-size > PAGE_SIZE with udmabuf.
That doesn't explain why this is required.
Please note that accessing the pages/folio of an sg-table returned by DMA-buf is illegal and strictly forbidden!
Regards, Christian.
Signed-off-by: Bobby Eshleman bobbyeshleman@meta.com
drivers/dma-buf/udmabuf.c | 47 ++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 42 insertions(+), 5 deletions(-)
diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c index 94b8ecb892bb..f28dd3788ada 100644 --- a/drivers/dma-buf/udmabuf.c +++ b/drivers/dma-buf/udmabuf.c @@ -141,26 +141,63 @@ 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. */ +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)-- 2.53.0-Meta