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    SubjectRe: [Xen-devel] [PATCH v2 5/9] xen/gntdev: Allow mappings for DMA buffers
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    On 06/04/2018 11:12 PM, Boris Ostrovsky wrote:
    > 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(). */
    >
    Ok
    >> + 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?
    It is possible to have vaddr == NULL and frames != NULL as we
    allocate frames outside of gnttab_dma_alloc_pages which
    may fail. Calling kfree on NULL pointer is safe, so
    I see no reason to change this code.
    >
    >> 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()?
    I'd love to, but pfn_to_mfn is only defined for x86, not ARM: [1] and [2]
    Thus,

    drivers/xen/gntdev.c:408:10: error: implicit declaration of function
    ‘pfn_to_mfn’ [-Werror=implicit-function-declaration]
        mfn = pfn_to_mfn(page_to_pfn(map->pages[i]));

    So, I'll keep __pfn_to_mfn
    >
    >
    > -boris
    Thank you,
    Oleksandr
    >> + 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__ */
    >
    > _______________________________________________
    > Xen-devel mailing list
    > Xen-devel@lists.xenproject.org
    > https://lists.xenproject.org/mailman/listinfo/xen-devel
    [1] https://elixir.bootlin.com/linux/v4.17/ident/pfn_to_mfn
    [2] https://elixir.bootlin.com/linux/v4.17/ident/__pfn_to_mfn

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