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

Oleksandr Andrushchenko
2018-06-06T08:14:16Z

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__ */
>
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[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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