Re: [PATCH v2 5/9] xen/gntdev: Allow mappings for DMA buffers

Boris Ostrovsky
2018-06-04T20:12:45Z

On 06/01/2018 07:41 AM, Oleksandr Andrushchenko wrote:
> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>
> Allow mappings for DMA backed buffers if grant table module
> supports such: this extends grant device to not only map buffers
> made of balloon pages, but also from buffers allocated with
> dma_alloc_xxx.
>
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
> ---
> drivers/xen/gntdev.c | 99 ++++++++++++++++++++++++++++++++++++++-
> include/uapi/xen/gntdev.h | 15 ++++++
> 2 files changed, 112 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index bd56653b9bbc..9813fc440c70 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -37,6 +37,9 @@
> #include <linux/slab.h>
> #include <linux/highmem.h>
> #include <linux/refcount.h>
> +#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
> +#include <linux/of_device.h>
> +#endif
>
> #include <xen/xen.h>
> #include <xen/grant_table.h>
> @@ -72,6 +75,11 @@ struct gntdev_priv {
> struct mutex lock;
> struct mm_struct *mm;
> struct mmu_notifier mn;
> +
> +#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
> + /* Device for which DMA memory is allocated. */
> + struct device *dma_dev;
> +#endif
> };
>
> struct unmap_notify {
> @@ -96,10 +104,27 @@ struct grant_map {
> struct gnttab_unmap_grant_ref *kunmap_ops;
> struct page **pages;
> unsigned long pages_vm_start;
> +
> +#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
> + /*
> + * If dmabuf_vaddr is not NULL then this mapping is backed by DMA
> + * capable memory.
> + */
> +
> + struct device *dma_dev;
> + /* Flags used to create this DMA buffer: GNTDEV_DMA_FLAG_XXX. */
> + int dma_flags;
> + void *dma_vaddr;
> + dma_addr_t dma_bus_addr;
> + /* This is required for gnttab_dma_{alloc|free}_pages. */

How about

/* Needed to avoid allocation in gnttab_dma_free_pages(). */

> + xen_pfn_t *frames;
> +#endif
> };
>
> static int unmap_grant_pages(struct grant_map *map, int offset, int pages);
>
> +static struct miscdevice gntdev_miscdev;
> +
> /* ------------------------------------------------------------------ */
>
> static void gntdev_print_maps(struct gntdev_priv *priv,
> @@ -121,8 +146,27 @@ static void gntdev_free_map(struct grant_map *map)
> if (map == NULL)
> return;
>
> +#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
> + if (map->dma_vaddr) {
> + struct gnttab_dma_alloc_args args;
> +
> + args.dev = map->dma_dev;
> + args.coherent = map->dma_flags & GNTDEV_DMA_FLAG_COHERENT;
> + args.nr_pages = map->count;
> + args.pages = map->pages;
> + args.frames = map->frames;
> + args.vaddr = map->dma_vaddr;
> + args.dev_bus_addr = map->dma_bus_addr;
> +
> + gnttab_dma_free_pages(&args);
> + } else
> +#endif
> if (map->pages)
> gnttab_free_pages(map->count, map->pages);
> +
> +#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
> + kfree(map->frames);
> +#endif

Can this be done under if (map->dma_vaddr) ? In other words, is it
possible for dma_vaddr to be NULL and still have unallocated frames pointer?

> kfree(map->pages);
> kfree(map->grants);
> kfree(map->map_ops);
> @@ -132,7 +176,8 @@ static void gntdev_free_map(struct grant_map *map)
> kfree(map);
> }
>
> -static struct grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count)
> +static struct grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count,
> + int dma_flags)
> {
> struct grant_map *add;
> int i;
> @@ -155,6 +200,37 @@ static struct grant_map *gntdev_alloc_map(struct gntdev_priv *priv, int count)
> NULL == add->pages)
> goto err;
>
> +#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
> + add->dma_flags = dma_flags;
> +
> + /*
> + * Check if this mapping is requested to be backed
> + * by a DMA buffer.
> + */
> + if (dma_flags & (GNTDEV_DMA_FLAG_WC | GNTDEV_DMA_FLAG_COHERENT)) {
> + struct gnttab_dma_alloc_args args;
> +
> + add->frames = kcalloc(count, sizeof(add->frames[0]),
> + GFP_KERNEL);
> + if (!add->frames)
> + goto err;
> +
> + /* Remember the device, so we can free DMA memory. */
> + add->dma_dev = priv->dma_dev;
> +
> + args.dev = priv->dma_dev;
> + args.coherent = dma_flags & GNTDEV_DMA_FLAG_COHERENT;
> + args.nr_pages = count;
> + args.pages = add->pages;
> + args.frames = add->frames;
> +
> + if (gnttab_dma_alloc_pages(&args))
> + goto err;
> +
> + add->dma_vaddr = args.vaddr;
> + add->dma_bus_addr = args.dev_bus_addr;
> + } else
> +#endif
> if (gnttab_alloc_pages(count, add->pages))
> goto err;
>
> @@ -325,6 +401,14 @@ static int map_grant_pages(struct grant_map *map)
> map->unmap_ops[i].handle = map->map_ops[i].handle;
> if (use_ptemod)
> map->kunmap_ops[i].handle = map->kmap_ops[i].handle;
> +#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
> + else if (map->dma_vaddr) {
> + unsigned long mfn;
> +
> + mfn = __pfn_to_mfn(page_to_pfn(map->pages[i]));

Not pfn_to_mfn()?

-boris

> + map->unmap_ops[i].dev_bus_addr = __pfn_to_phys(mfn);
> + }
> +#endif
> }
> return err;
> }
> @@ -548,6 +632,17 @@ static int gntdev_open(struct inode *inode, struct file *flip)
> }
>
> flip->private_data = priv;
> +#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
> + priv->dma_dev = gntdev_miscdev.this_device;
> +
> + /*
> + * The device is not spawn from a device tree, so arch_setup_dma_ops
> + * is not called, thus leaving the device with dummy DMA ops.
> + * Fix this call of_dma_configure() with a NULL node to set
> + * default DMA ops.
> + */
> + of_dma_configure(priv->dma_dev, NULL);
> +#endif
> pr_debug("priv %p\n", priv);
>
> return 0;
> @@ -589,7 +684,7 @@ static long gntdev_ioctl_map_grant_ref(struct gntdev_priv *priv,
> return -EINVAL;
>
> err = -ENOMEM;
> - map = gntdev_alloc_map(priv, op.count);
> + map = gntdev_alloc_map(priv, op.count, 0 /* This is not a dma-buf. */);
> if (!map)
> return err;
>
> diff --git a/include/uapi/xen/gntdev.h b/include/uapi/xen/gntdev.h
> index 6d1163456c03..4b9d498a31d4 100644
> --- a/include/uapi/xen/gntdev.h
> +++ b/include/uapi/xen/gntdev.h
> @@ -200,4 +200,19 @@ struct ioctl_gntdev_grant_copy {
> /* Send an interrupt on the indicated event channel */
> #define UNMAP_NOTIFY_SEND_EVENT 0x2
>
> +/*
> + * Flags to be used while requesting memory mapping's backing storage
> + * to be allocated with DMA API.
> + */
> +
> +/*
> + * The buffer is backed with memory allocated with dma_alloc_wc.
> + */
> +#define GNTDEV_DMA_FLAG_WC (1 << 0)
> +
> +/*
> + * The buffer is backed with memory allocated with dma_alloc_coherent.
> + */
> +#define GNTDEV_DMA_FLAG_COHERENT (1 << 1)
> +
> #endif /* __LINUX_PUBLIC_GNTDEV_H__ */