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Re: [Xen-devel] [PATCH v2 5/9] xen/gntdev: Allow mappings for DMA buffers
- To: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, dri-devel@xxxxxxxxxxxxxxxxxxxxx, linux-media@xxxxxxxxxxxxxxx, jgross@xxxxxxxx, konrad.wilk@xxxxxxxxxx, Stefano Stabellini <sstabellini@xxxxxxxxxx>
- From: Oleksandr Andrushchenko <andr2000@xxxxxxxxx>
- Date: Fri, 8 Jun 2018 14:33:46 +0300
- Cc: daniel.vetter@xxxxxxxxx, matthew.d.roper@xxxxxxxxx, dongwon.kim@xxxxxxxxx, Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
- Delivery-date: Fri, 08 Jun 2018 11:34:06 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 06/08/2018 12:46 AM, Boris Ostrovsky wrote:
(Stefano, question for you at the end)
On 06/07/2018 02:39 AM, Oleksandr Andrushchenko wrote:
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.
I was only thinking of option 2. But if it is possible to have frames !=
NULL and dma_vaddr == NULL then perhaps we indeed will have to live with
the extra ifdef.
ok
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
I'd rather fix it in ARM code. Stefano, why does ARM uses the
underscored version?
Do you want me to add one more patch for ARM to wrap __pfn_to_mfn
with static inline for ARM? e.g.
static inline ...pfn_to_mfn(...)
{
__pfn_to_mfn();
}
-boris
Thank you,
Oleksandr
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