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


  • To: Oleksandr Andrushchenko <andr2000@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, dri-devel@xxxxxxxxxxxxxxxxxxxxx, linux-media@xxxxxxxxxxxxxxx, jgross@xxxxxxxx, konrad.wilk@xxxxxxxxxx
  • From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
  • Date: Wed, 6 Jun 2018 17:19:51 -0400
  • Autocrypt: addr=boris.ostrovsky@xxxxxxxxxx; prefer-encrypt=mutual; keydata= xsFNBFH8CgsBEAC0KiOi9siOvlXatK2xX99e/J3OvApoYWjieVQ9232Eb7GzCWrItCzP8FUV PQg8rMsSd0OzIvvjbEAvaWLlbs8wa3MtVLysHY/DfqRK9Zvr/RgrsYC6ukOB7igy2PGqZd+M MDnSmVzik0sPvB6xPV7QyFsykEgpnHbvdZAUy/vyys8xgT0PVYR5hyvhyf6VIfGuvqIsvJw5 C8+P71CHI+U/IhsKrLrsiYHpAhQkw+Zvyeml6XSi5w4LXDbF+3oholKYCkPwxmGdK8MUIdkM d7iYdKqiP4W6FKQou/lC3jvOceGupEoDV9botSWEIIlKdtm6C4GfL45RD8V4B9iy24JHPlom woVWc0xBZboQguhauQqrBFooHO3roEeM1pxXjLUbDtH4t3SAI3gt4dpSyT3EvzhyNQVVIxj2 FXnIChrYxR6S0ijSqUKO0cAduenhBrpYbz9qFcB/GyxD+ZWY7OgQKHUZMWapx5bHGQ8bUZz2 SfjZwK+GETGhfkvNMf6zXbZkDq4kKB/ywaKvVPodS1Poa44+B9sxbUp1jMfFtlOJ3AYB0WDS Op3d7F2ry20CIf1Ifh0nIxkQPkTX7aX5rI92oZeu5u038dHUu/dO2EcuCjl1eDMGm5PLHDSP 0QUw5xzk1Y8MG1JQ56PtqReO33inBXG63yTIikJmUXFTw6lLJwARAQABzTNCb3JpcyBPc3Ry b3Zza3kgKFdvcmspIDxib3Jpcy5vc3Ryb3Zza3lAb3JhY2xlLmNvbT7CwXgEEwECACIFAlH8 CgsCGwMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEIredpCGysGyasEP/j5xApopUf4g 9Fl3UxZuBx+oduuw3JHqgbGZ2siA3EA4bKwtKq8eT7ekpApn4c0HA8TWTDtgZtLSV5IdH+9z JimBDrhLkDI3Zsx2CafL4pMJvpUavhc5mEU8myp4dWCuIylHiWG65agvUeFZYK4P33fGqoaS VGx3tsQIAr7MsQxilMfRiTEoYH0WWthhE0YVQzV6kx4wj4yLGYPPBtFqnrapKKC8yFTpgjaK jImqWhU9CSUAXdNEs/oKVR1XlkDpMCFDl88vKAuJwugnixjbPFTVPyoC7+4Bm/FnL3iwlJVE qIGQRspt09r+datFzPqSbp5Fo/9m4JSvgtPp2X2+gIGgLPWp2ft1NXHHVWP19sPgEsEJXSr9 tskM8ScxEkqAUuDs6+x/ISX8wa5Pvmo65drN+JWA8EqKOHQG6LUsUdJolFM2i4Z0k40BnFU/ kjTARjrXW94LwokVy4x+ZYgImrnKWeKac6fMfMwH2aKpCQLlVxdO4qvJkv92SzZz4538az1T m+3ekJAimou89cXwXHCFb5WqJcyjDfdQF857vTn1z4qu7udYCuuV/4xDEhslUq1+GcNDjAhB nNYPzD+SvhWEsrjuXv+fDONdJtmLUpKs4Jtak3smGGhZsqpcNv8nQzUGDQZjuCSmDqW8vn2o hWwveNeRTkxh+2x1Qb3GT46uzsFNBFH8CgsBEADGC/yx5ctcLQlB9hbq7KNqCDyZNoYu1HAB Hal3MuxPfoGKObEktawQPQaSTB5vNlDxKihezLnlT/PKjcXC2R1OjSDinlu5XNGc6mnky03q yymUPyiMtWhBBftezTRxWRslPaFWlg/h/Y1iDuOcklhpr7K1h1jRPCrf1yIoxbIpDbffnuyz kuto4AahRvBU4Js4sU7f/btU+h+e0AcLVzIhTVPIz7PM+Gk2LNzZ3/on4dnEc/qd+ZZFlOQ4 KDN/hPqlwA/YJsKzAPX51L6Vv344pqTm6Z0f9M7YALB/11FO2nBB7zw7HAUYqJeHutCwxm7i BDNt0g9fhviNcJzagqJ1R7aPjtjBoYvKkbwNu5sWDpQ4idnsnck4YT6ctzN4I+6lfkU8zMzC gM2R4qqUXmxFIS4Bee+gnJi0Pc3KcBYBZsDK44FtM//5Cp9DrxRQOh19kNHBlxkmEb8kL/pw XIDcEq8MXzPBbxwHKJ3QRWRe5jPNpf8HCjnZz0XyJV0/4M1JvOua7IZftOttQ6KnM4m6WNIZ 2ydg7dBhDa6iv1oKdL7wdp/rCulVWn8R7+3cRK95SnWiJ0qKDlMbIN8oGMhHdin8cSRYdmHK kTnvSGJNlkis5a+048o0C6jI3LozQYD/W9wq7MvgChgVQw1iEOB4u/3FXDEGulRVko6xCBU4 SQARAQABwsFfBBgBAgAJBQJR/AoLAhsMAAoJEIredpCGysGyfvMQAIywR6jTqix6/fL0Ip8G jpt3uk//QNxGJE3ZkUNLX6N786vnEJvc1beCu6EwqD1ezG9fJKMl7F3SEgpYaiKEcHfoKGdh 30B3Hsq44vOoxR6zxw2B/giADjhmWTP5tWQ9548N4VhIZMYQMQCkdqaueSL+8asp8tBNP+TJ PAIIANYvJaD8xA7sYUXGTzOXDh2THWSvmEWWmzok8er/u6ZKdS1YmZkUy8cfzrll/9hiGCTj u3qcaOM6i/m4hqtvsI1cOORMVwjJF4+IkC5ZBoeRs/xW5zIBdSUoC8L+OCyj5JETWTt40+lu qoqAF/AEGsNZTrwHJYu9rbHH260C0KYCNqmxDdcROUqIzJdzDKOrDmebkEVnxVeLJBIhYZUd t3Iq9hdjpU50TA6sQ3mZxzBdfRgg+vaj2DsJqI5Xla9QGKD+xNT6v14cZuIMZzO7w0DoojM4 ByrabFsOQxGvE0w9Dch2BDSI2Xyk1zjPKxG1VNBQVx3flH37QDWpL2zlJikW29Ws86PHdthh Fm5PY8YtX576DchSP6qJC57/eAAe/9ztZdVAdesQwGb9hZHJc75B+VNm4xrh/PJO6c1THqdQ 19WVJ+7rDx3PhVncGlbAOiiiE3NOFPJ1OQYxPKtpBUukAlOTnkKE6QcA4zckFepUkfmBV1wM Jg6OxFYd01z+a+oL
  • Cc: daniel.vetter@xxxxxxxxx, matthew.d.roper@xxxxxxxxx, dongwon.kim@xxxxxxxxx, Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
  • Delivery-date: Wed, 06 Jun 2018 21:16:21 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

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
>> +    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);
>> +    } 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.


> 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))
>>> +            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?

-boris



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