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Date: Thu, 7 Jun 2018 09:39:03 +0300
From: Oleksandr Andrushchenko <andr2000@...il.com>
To: Boris Ostrovsky <boris.ostrovsky@...cle.com>,
xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
dri-devel@...ts.freedesktop.org, linux-media@...r.kernel.org,
jgross@...e.com, konrad.wilk@...cle.com
Cc: daniel.vetter@...el.com, matthew.d.roper@...el.com,
dongwon.kim@...el.com,
Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
Subject: Re: [Xen-devel] [PATCH v2 5/9] xen/gntdev: Allow mappings for DMA
buffers
On 06/07/2018 12:19 AM, Boris Ostrovsky wrote:
> 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)
>>> if (map == NULL)
>>> return;
>>> +#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
*Option 1: kfree(map->frames);*
>>> + 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);
*Option 2: kfree(map->frames);*
>>> + } 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,
>
> I am not questioning safety of the code, I would like avoid another ifdef.
Ah, I now understand, so you are asking if we can have
that kfree(map->frames); in the place *Option 2* I marked above.
Unfortunately no: map->frames is allocated before we try to
allocate DMA memory, e.g. before dma_vaddr is set:
[...]
add->frames = kcalloc(count, sizeof(add->frames[0]),
GFP_KERNEL);
if (!add->frames)
goto err;
[...]
if (gnttab_dma_alloc_pages(&args))
goto err;
add->dma_vaddr = args.vaddr;
[...]
err:
gntdev_free_map(add);
So, it is possible to enter gntdev_free_map with
frames != NULL and dma_vaddr == NULL. Option 1 above cannot be used
as map->frames is needed for gnttab_dma_free_pages(&args);
and Option 2 cannot be used as frames != NULL and dma_vaddr == NULL.
Thus, I think that unfortunately we need that #ifdef.
Option 3 below can also be considered, but that seems to be not good
as we free resources in different places which looks inconsistent.
Sorry if I'm still missing your point.
>
>> 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))
*Option 3: kfree(map->frames);*
>>>> + 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
>
> How will this work on non-PV x86?
So, you mean I need:
#ifdef CONFIG_X86
mfn = pfn_to_mfn(page_to_pfn(map->pages[i]));
#else
mfn = __pfn_to_mfn(page_to_pfn(map->pages[i]));
#endif
> -boris
>
>
Thank you,
Oleksandr
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