Messages in this thread Patch in this message | | | Subject | Re: [Xen-devel] [PATCH v2 5/9] xen/gntdev: Allow mappings for DMA buffers | From | Oleksandr Andrushchenko <> | Date | Thu, 7 Jun 2018 09:39:03 +0300 |
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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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