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

[Boris Ostrovsky]

On 06/06/2018 04:14 AM, Oleksandr Andrushchenko wrote:
> On 06/04/2018 11:12 PM, Boris Ostrovsky wrote:
>> On 06/01/2018 07:41 AM, Oleksandr Andrushchenko wrote:

>> @@ -121,8 +146,27 @@ static void gntdev_free_map(struct grant_map *map)
>> ÂÂÂÂÂ if (map == NULL)
>> ÂÂÂÂÂÂÂÂÂ return;
>> Â +#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
>> +ÂÂÂ if (map->dma_vaddr) {
>> +ÂÂÂÂÂÂÂ struct gnttab_dma_alloc_args args;
>> +
>> +ÂÂÂÂÂÂÂ args.dev = map->dma_dev;
>> +ÂÂÂÂÂÂÂ args.coherent = map->dma_flags & GNTDEV_DMA_FLAG_COHERENT;
>> +ÂÂÂÂÂÂÂ args.nr_pages = map->count;
>> +ÂÂÂÂÂÂÂ args.pages = map->pages;
>> +ÂÂÂÂÂÂÂ args.frames = map->frames;
>> +ÂÂÂÂÂÂÂ args.vaddr = map->dma_vaddr;
>> +ÂÂÂÂÂÂÂ args.dev_bus_addr = map->dma_bus_addr;
>> +
>> +ÂÂÂÂÂÂÂ gnttab_dma_free_pages(&args);
>> +ÂÂÂ } else
>> +#endif
>> ÂÂÂÂÂ if (map->pages)
>> ÂÂÂÂÂÂÂÂÂ gnttab_free_pages(map->count, map->pages);
>> +
>> +#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
>> +ÂÂÂ kfree(map->frames);
>> +#endif
>>
>> Can this be done under if (map->dma_vaddr) ?
>
>> Â 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,


I am not questioning safety of the code, I would like avoid another ifdef.


> so
> I see no reason to change this code.
>>
>>> ÂÂÂÂÂ kfree(map->pages);
>>> ÂÂÂÂÂ kfree(map->grants);
>>> ÂÂÂÂÂ kfree(map->map_ops);
>>> @@ -132,7 +176,8 @@ static void gntdev_free_map(struct grant_map *map)
>>> ÂÂÂÂÂ kfree(map);
>>> Â }
>>> Â -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,
>>> +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ int dma_flags)
>>> Â {
>>> ÂÂÂÂÂ struct grant_map *add;
>>> ÂÂÂÂÂ int i;
>>> @@ -155,6 +200,37 @@ static struct grant_map
>>> *gntdev_alloc_map(struct gntdev_priv *priv, int count)
>>> ÂÂÂÂÂÂÂÂÂ NULL == add->pages)
>>> ÂÂÂÂÂÂÂÂÂ goto err;
>>> Â +#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
>>> +ÂÂÂ add->dma_flags = dma_flags;
>>> +
>>> +ÂÂÂ /*
>>> +ÂÂÂÂ * Check if this mapping is requested to be backed
>>> +ÂÂÂÂ * by a DMA buffer.
>>> +ÂÂÂÂ */
>>> +ÂÂÂ if (dma_flags & (GNTDEV_DMA_FLAG_WC | GNTDEV_DMA_FLAG_COHERENT)) {
>>> +ÂÂÂÂÂÂÂ struct gnttab_dma_alloc_args args;
>>> +
>>> +ÂÂÂÂÂÂÂ add->frames = kcalloc(count, sizeof(add->frames[0]),
>>> +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ GFP_KERNEL);
>>> +ÂÂÂÂÂÂÂ if (!add->frames)
>>> +ÂÂÂÂÂÂÂÂÂÂÂ goto err;
>>> +
>>> +ÂÂÂÂÂÂÂ /* Remember the device, so we can free DMA memory. */
>>> +ÂÂÂÂÂÂÂ add->dma_dev = priv->dma_dev;
>>> +
>>> +ÂÂÂÂÂÂÂ args.dev = priv->dma_dev;
>>> +ÂÂÂÂÂÂÂ args.coherent = dma_flags & GNTDEV_DMA_FLAG_COHERENT;
>>> +ÂÂÂÂÂÂÂ args.nr_pages = count;
>>> +ÂÂÂÂÂÂÂ args.pages = add->pages;
>>> +ÂÂÂÂÂÂÂ args.frames = add->frames;
>>> +
>>> +ÂÂÂÂÂÂÂ if (gnttab_dma_alloc_pages(&args))
>>> +ÂÂÂÂÂÂÂÂÂÂÂ goto err;
>>> +
>>> +ÂÂÂÂÂÂÂ add->dma_vaddr = args.vaddr;
>>> +ÂÂÂÂÂÂÂ add->dma_bus_addr = args.dev_bus_addr;
>>> +ÂÂÂ } else
>>> +#endif
>>> ÂÂÂÂÂ if (gnttab_alloc_pages(count, add->pages))
>>> ÂÂÂÂÂÂÂÂÂ goto err;
>>> Â @@ -325,6 +401,14 @@ static int map_grant_pages(struct grant_map
>>> *map)
>>> ÂÂÂÂÂÂÂÂÂ map->unmap_ops[i].handle = map->map_ops[i].handle;
>>> ÂÂÂÂÂÂÂÂÂ if (use_ptemod)
>>> ÂÂÂÂÂÂÂÂÂÂÂÂÂ map->kunmap_ops[i].handle = map->kmap_ops[i].handle;
>>> +#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
>>> +ÂÂÂÂÂÂÂ else if (map->dma_vaddr) {
>>> +ÂÂÂÂÂÂÂÂÂÂÂ unsigned long mfn;
>>> +
>>> +ÂÂÂÂÂÂÂÂÂÂÂ 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
> âpfn_to_mfnâ [-Werror=implicit-function-declaration]
> ÂÂÂ mfn = pfn_to_mfn(page_to_pfn(map->pages[i]));
>
> So, I'll keep __pfn_to_mfn


How will this work on non-PV x86?

-boris