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