io_uring/zcrx: allocate sgtable for umem areas

Currently, dma addresses for umem areas are stored directly in niovs.
It's memory efficient but inconvenient. I need a better format 1) to
share code with dmabuf areas, and 2) for disentangling page, folio and
niov sizes. dmabuf already provides sg_table, create one for user memory
as well.

Signed-off-by: Pavel Begunkov <[email protected]>
Reviewed-by: David Wei <[email protected]>
Link: https://lore.kernel.org/r/f3c15081827c1bf5427d3a2e693bc526476b87ee.1751466461.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <[email protected]>

Author: isilence

io_uring/zcrx.c

@@ -161,7 +161,7 @@ static int io_import_umem(struct io_zcrx_ifq *ifq,
 			  struct io_uring_zcrx_area_reg *area_reg)
 {
 	struct page **pages;
-	int nr_pages;
+	int nr_pages, ret;
 
 	if (area_reg->dmabuf_fd)
 		return -EINVAL;
@@ -172,6 +172,12 @@ static int io_import_umem(struct io_zcrx_ifq *ifq,
 	if (IS_ERR(pages))
 		return PTR_ERR(pages);
 
+	ret = sg_alloc_table_from_pages(&mem->page_sg_table, pages, nr_pages,
+					0, nr_pages << PAGE_SHIFT,
+					GFP_KERNEL_ACCOUNT);
+	if (ret)
+		return ret;
+
 	mem->pages = pages;
 	mem->nr_folios = nr_pages;
 	mem->size = area_reg->len;
@@ -186,6 +192,7 @@ static void io_release_area_mem(struct io_zcrx_mem *mem)
 	}
 	if (mem->pages) {
 		unpin_user_pages(mem->pages, mem->nr_folios);
+		sg_free_table(&mem->page_sg_table);
 		kvfree(mem->pages);
 	}
 }
@@ -207,67 +214,36 @@ static int io_import_area(struct io_zcrx_ifq *ifq,
 	return io_import_umem(ifq, mem, area_reg);
 }
 
-static void io_zcrx_unmap_umem(struct io_zcrx_ifq *ifq,
-				struct io_zcrx_area *area, int nr_mapped)
-{
-	int i;
-
-	for (i = 0; i < nr_mapped; i++) {
-		netmem_ref netmem = net_iov_to_netmem(&area->nia.niovs[i]);
-		dma_addr_t dma = page_pool_get_dma_addr_netmem(netmem);
-
-		dma_unmap_page_attrs(ifq->dev, dma, PAGE_SIZE,
-				     DMA_FROM_DEVICE, IO_DMA_ATTR);
-	}
-}
-
-static void __io_zcrx_unmap_area(struct io_zcrx_ifq *ifq,
-				 struct io_zcrx_area *area, int nr_mapped)
+static void io_zcrx_unmap_area(struct io_zcrx_ifq *ifq,
+				struct io_zcrx_area *area)
 {
 	int i;
 
-	if (area->mem.is_dmabuf)
-		io_release_dmabuf(&area->mem);
-	else
-		io_zcrx_unmap_umem(ifq, area, nr_mapped);
+	guard(mutex)(&ifq->dma_lock);
+	if (!area->is_mapped)
+		return;
+	area->is_mapped = false;
 
 	for (i = 0; i < area->nia.num_niovs; i++)
 		net_mp_niov_set_dma_addr(&area->nia.niovs[i], 0);
-}
-
-static void io_zcrx_unmap_area(struct io_zcrx_ifq *ifq, struct io_zcrx_area *area)
-{
-	guard(mutex)(&ifq->dma_lock);
 
-	if (area->is_mapped)
-		__io_zcrx_unmap_area(ifq, area, area->nia.num_niovs);
-	area->is_mapped = false;
+	if (area->mem.is_dmabuf) {
+		io_release_dmabuf(&area->mem);
+	} else {
+		dma_unmap_sgtable(ifq->dev, &area->mem.page_sg_table,
+				  DMA_FROM_DEVICE, IO_DMA_ATTR);
+	}
 }
 
-static int io_zcrx_map_area_umem(struct io_zcrx_ifq *ifq, struct io_zcrx_area *area)
+static unsigned io_zcrx_map_area_umem(struct io_zcrx_ifq *ifq, struct io_zcrx_area *area)
 {
-	int i;
-
-	for (i = 0; i < area->nia.num_niovs; i++) {
-		struct net_iov *niov = &area->nia.niovs[i];
-		dma_addr_t dma;
-
-		dma = dma_map_page_attrs(ifq->dev, area->mem.pages[i], 0,
-					 PAGE_SIZE, DMA_FROM_DEVICE, IO_DMA_ATTR);
-		if (dma_mapping_error(ifq->dev, dma))
-			break;
-		if (net_mp_niov_set_dma_addr(niov, dma)) {
-			dma_unmap_page_attrs(ifq->dev, dma, PAGE_SIZE,
-					     DMA_FROM_DEVICE, IO_DMA_ATTR);
-			break;
-		}
-	}
+	int ret;
 
-	if (i != area->nia.num_niovs) {
-		__io_zcrx_unmap_area(ifq, area, i);
-		return -EINVAL;
-	}
-	return 0;
+	ret = dma_map_sgtable(ifq->dev, &area->mem.page_sg_table,
+				DMA_FROM_DEVICE, IO_DMA_ATTR);
+	if (ret < 0)
+		return ret;
+	return io_populate_area_dma(ifq, area, &area->mem.page_sg_table, 0);
 }
 
 static int io_zcrx_map_area(struct io_zcrx_ifq *ifq, struct io_zcrx_area *area)

io_uring/zcrx.h

@@ -14,6 +14,7 @@ struct io_zcrx_mem {
 
 	struct page			**pages;
 	unsigned long			nr_folios;
+	struct sg_table			page_sg_table;
 
 	struct dma_buf_attachment	*attach;
 	struct dma_buf			*dmabuf;