From mboxrd@z Thu Jan 1 00:00:00 1970 From: Boris Ostrovsky Subject: Re: [Xen-devel] [PATCH v2 5/9] xen/gntdev: Allow mappings for DMA buffers Date: Thu, 7 Jun 2018 17:46:53 -0400 Message-ID: <78dc2fc4-cdac-05b7-2c34-22b69e7e009c@oracle.com> References: <20180601114132.22596-1-andr2000@gmail.com> <20180601114132.22596-6-andr2000@gmail.com> <64facf05-0a51-c3d9-9d3b-780893248628@oracle.com> <84217eac-b83b-710f-39ab-c93cad65bf9a@gmail.com> <30fa03c0-1b75-c0b1-b14f-8b52ea584e20@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <30fa03c0-1b75-c0b1-b14f-8b52ea584e20@gmail.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Oleksandr Andrushchenko , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org, jgross@suse.com, konrad.wilk@oracle.com, Stefano Stabellini Cc: daniel.vetter@intel.com, matthew.d.roper@intel.com, dongwon.kim@intel.com, Oleksandr Andrushchenko List-Id: dri-devel@lists.freedesktop.org (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. > > 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? -boris