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Date: Tue, 18 Dec 2018 13:40:48 +0000
From: Tariq Toukan <tariqt@...lanox.com>
To: Stephen Warren <swarren@...dotorg.org>,
"Wei@...dotorg.org" <Wei@...dotorg.org>,
"Hu@...dotorg.org" <Hu@...dotorg.org>,
"\\ (Xavier\\)" <xavier.huwei@...wei.com>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
Doug Ledford <dledford@...hat.com>,
Jason Gunthorpe <jgg@...lanox.com>,
Stephen Warren <swarren@...dia.com>
Subject: RE: [RFC PATCH] net/mlx4: Get rid of page operation after
dma_alloc_coherent
Hi Stephen,
Thanks for your patch.
> -----Original Message-----
> From: linux-rdma-owner@...r.kernel.org [mailto:linux-rdma-
> owner@...r.kernel.org] On Behalf Of Stephen Warren
> Sent: Saturday, December 15, 2018 1:33 AM
> To: Tariq Toukan <tariqt@...lanox.com>; Wei@...dotorg.org;
> Hu@...dotorg.org; \ (Xavier\) <xavier.huwei@...wei.com>
> Cc: netdev@...r.kernel.org; linux-rdma@...r.kernel.org; Doug Ledford
> <dledford@...hat.com>; Jason Gunthorpe <jgg@...lanox.com>; Stephen
> Warren <swarren@...dia.com>
> Subject: [RFC PATCH] net/mlx4: Get rid of page operation after
> dma_alloc_coherent
>
> From: Stephen Warren <swarren@...dia.com>
>
> This is a port of commit 378efe798ecf ("RDMA/hns: Get rid of page operation
> after dma_alloc_coherent") to the mlx4 driver. That change was described
> as:
>
> > In general, dma_alloc_coherent() returns a CPU virtual address and a
> > DMA address, and we have no guarantee that the underlying memory
> even
> > has an associated struct page at all.
> >
> > This patch gets rid of the page operation after dma_alloc_coherent,
> > and records the VA returned form dma_alloc_coherent in the struct of
> > hem in hns RoCE driver.
>
I need to review this patch first.
> Differences in this port relative to the hns patch:
>
> 1) The hns patch only needed to fix a dma_alloc_coherent path, but this
> patch also needs to fix an alloc_pages path. This appears to be simple except
> for the next point.
>
> 2) The hns patch converted a bunch of code to consistently use
> sg_dma_len(mem) rather than a mix of that and mem->length However, it
> seems that sg_dma_len(mem) can be modified or zeroed at runtime, and so
> using it when calling e.g. __free_pages is problematic. I suspect the same
> issue affects mlx4_table_find() somehow too, and similarly I expect the hns
> driver has an issue in this area. Instead, this patch converts everything to use
> mem->length instead. I'd like some feedback on this issue.
>
OK. I will carefully go over this point.
Thanks.
> Signed-off-by: Stephen Warren <swarren@...dia.com>
> ---
> Note: I've tested this patch in downstream 4.9 and 4.14 based kernels, but
> can't test it in mainline (at least ibping works) since my system isn't
> supported their yet. I have compile-tested it in mainline at least, for ARM64.
>
> drivers/net/ethernet/mellanox/mlx4/icm.c | 51 ++++++++++++++----------
> drivers/net/ethernet/mellanox/mlx4/icm.h | 1 +
> 2 files changed, 30 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx4/icm.c
> b/drivers/net/ethernet/mellanox/mlx4/icm.c
> index 4b4351141b94..b14207cef69e 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/icm.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/icm.c
> @@ -72,7 +72,7 @@ static void mlx4_free_icm_coherent(struct mlx4_dev
> *dev, struct mlx4_icm_chunk *
> for (i = 0; i < chunk->npages; ++i)
> dma_free_coherent(&dev->persist->pdev->dev,
> chunk->mem[i].length,
> - lowmem_page_address(sg_page(&chunk-
> >mem[i])),
> + chunk->buf[i],
> sg_dma_address(&chunk->mem[i]));
> }
>
> @@ -95,9 +95,11 @@ void mlx4_free_icm(struct mlx4_dev *dev, struct
> mlx4_icm *icm, int coherent)
> kfree(icm);
> }
>
> -static int mlx4_alloc_icm_pages(struct scatterlist *mem, int order,
> +static int mlx4_alloc_icm_pages(struct mlx4_icm_chunk *chunk, int
> +order,
> gfp_t gfp_mask, int node)
> {
> + struct scatterlist *mem = &chunk->mem[chunk->npages];
> + void **buf = &chunk->buf[chunk->npages];
> struct page *page;
>
> page = alloc_pages_node(node, gfp_mask, order); @@ -108,25
> +110,30 @@ static int mlx4_alloc_icm_pages(struct scatterlist *mem, int
> order,
> }
>
> sg_set_page(mem, page, PAGE_SIZE << order, 0);
> + *buf = lowmem_page_address(page);
> return 0;
> }
>
> -static int mlx4_alloc_icm_coherent(struct device *dev, struct scatterlist
> *mem,
> - int order, gfp_t gfp_mask)
> +static int mlx4_alloc_icm_coherent(struct device *dev,
> + struct mlx4_icm_chunk *chunk, int order,
> + gfp_t gfp_mask)
> {
> - void *buf = dma_alloc_coherent(dev, PAGE_SIZE << order,
> - &sg_dma_address(mem), gfp_mask);
> - if (!buf)
> + struct scatterlist *mem = &chunk->mem[chunk->npages];
> + void **buf = &chunk->buf[chunk->npages];
> +
> + *buf = dma_alloc_coherent(dev, PAGE_SIZE << order,
> + &sg_dma_address(mem), gfp_mask);
> + if (!*buf)
> return -ENOMEM;
>
> - if (offset_in_page(buf)) {
> + if (offset_in_page(*buf)) {
> dma_free_coherent(dev, PAGE_SIZE << order,
> - buf, sg_dma_address(mem));
> + *buf, sg_dma_address(mem));
> return -ENOMEM;
> }
>
> - sg_set_buf(mem, buf, PAGE_SIZE << order);
> sg_dma_len(mem) = PAGE_SIZE << order;
> + mem->length = PAGE_SIZE << order;
> return 0;
> }
>
> @@ -174,6 +181,7 @@ struct mlx4_icm *mlx4_alloc_icm(struct mlx4_dev
> *dev, int npages,
> sg_init_table(chunk->mem,
> MLX4_ICM_CHUNK_LEN);
> chunk->npages = 0;
> chunk->nsg = 0;
> + memset(chunk->buf, 0, sizeof(chunk->buf));
> list_add_tail(&chunk->list, &icm->chunk_list);
> }
>
> @@ -186,11 +194,9 @@ struct mlx4_icm *mlx4_alloc_icm(struct mlx4_dev
> *dev, int npages,
>
> if (coherent)
> ret = mlx4_alloc_icm_coherent(&dev->persist-
> >pdev->dev,
> - &chunk->mem[chunk-
> >npages],
> - cur_order, mask);
> + chunk, cur_order, mask);
> else
> - ret = mlx4_alloc_icm_pages(&chunk->mem[chunk-
> >npages],
> - cur_order, mask,
> + ret = mlx4_alloc_icm_pages(chunk, cur_order, mask,
> dev->numa_node);
>
> if (ret) {
> @@ -316,11 +322,11 @@ void mlx4_table_put(struct mlx4_dev *dev, struct
> mlx4_icm_table *table, u32 obj) void *mlx4_table_find(struct
> mlx4_icm_table *table, u32 obj,
> dma_addr_t *dma_handle)
> {
> - int offset, dma_offset, i;
> + int offset, dma_offset, i, length;
> u64 idx;
> struct mlx4_icm_chunk *chunk;
> struct mlx4_icm *icm;
> - struct page *page = NULL;
> + void *addr = NULL;
>
> if (!table->lowmem)
> return NULL;
> @@ -336,28 +342,29 @@ void *mlx4_table_find(struct mlx4_icm_table
> *table, u32 obj,
>
> list_for_each_entry(chunk, &icm->chunk_list, list) {
> for (i = 0; i < chunk->npages; ++i) {
> + length = chunk->mem[i].length;
> if (dma_handle && dma_offset >= 0) {
> - if (sg_dma_len(&chunk->mem[i]) >
> dma_offset)
> + if (length > dma_offset)
> *dma_handle =
> sg_dma_address(&chunk->mem[i]) +
> dma_offset;
> - dma_offset -= sg_dma_len(&chunk-
> >mem[i]);
> + dma_offset -= length;
> }
> /*
> * DMA mapping can merge pages but not split them,
> * so if we found the page, dma_handle has already
> * been assigned to.
> */
> - if (chunk->mem[i].length > offset) {
> - page = sg_page(&chunk->mem[i]);
> + if (length > offset) {
> + addr = chunk->buf[i] + offset;
> goto out;
> }
> - offset -= chunk->mem[i].length;
> + offset -= length;
> }
> }
>
> out:
> mutex_unlock(&table->mutex);
> - return page ? lowmem_page_address(page) + offset : NULL;
> + return addr;
> }
>
> int mlx4_table_get_range(struct mlx4_dev *dev, struct mlx4_icm_table
> *table, diff --git a/drivers/net/ethernet/mellanox/mlx4/icm.h
> b/drivers/net/ethernet/mellanox/mlx4/icm.h
> index c9169a490557..a565188dc391 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/icm.h
> +++ b/drivers/net/ethernet/mellanox/mlx4/icm.h
> @@ -52,6 +52,7 @@ struct mlx4_icm_chunk {
> int npages;
> int nsg;
> struct scatterlist mem[MLX4_ICM_CHUNK_LEN];
> + void *buf[MLX4_ICM_CHUNK_LEN];
> };
>
> struct mlx4_icm {
> --
> 2.19.2
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