Em Thu, 18 Apr 2013 08:21:21 -0300 Mauro Carvalho Chehab <mchehab@xxxxxxxxxx> escreveu: > Em Thu, 18 Apr 2013 10:17:14 +0530 > Prabhakar Lad <prabhakar.csengg@xxxxxxxxx> escreveu: > > > Hi Marek, > > > > On Tue, Apr 16, 2013 at 4:48 PM, Laurent Pinchart > > <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > > > Hi Prabhakar, > > ... > > > >> *nbuffers = config_params.min_numbuffers; > > >> > > >> *nplanes = 1; > > >> + size = PAGE_ALIGN(size); > > > > > > I wonder if that's the best fix. > > > The queue_setup operation is supposed to return the size required by the > > > driver for each plane. Depending on the hardware requirements, that size might > > > not be a multiple of the page size. > > > > > > As we can't mmap() a fraction of a page, the allocated plane size needs to be > > > rounded up to the next page boundary to allow mmap() support. The dma-contig > > > and dma-sg allocators already do so in their alloc operation, but the vmalloc > > > allocator doesn't. > > > > > > The recent "media: vb2: add length check for mmap" patch verifies that the > > > mmap() size requested by userspace doesn't exceed the buffer size. As the > > > mmap() size is rounded up to the next page boundary the check will fail for > > > buffer sizes that are not multiple of the page size. > > > > > > Your fix will not result in overallocation (as the allocator already rounds > > > the size up), but will prevent the driver from importing a buffer large enough > > > for the hardware but not rounded up to the page size. > > > > > > A better fix might be to round up the buffer size in the buffer size check at > > > mmap() time, and fix the vmalloc allocator to round up the size. That the > > > allocator, not drivers, is responsible for buffer size alignment should be > > > documented in videobuf2-core.h. > > > > > > Do you plan to post a patch fixing it as per Laurent's suggestion ? > > I agree with Laurent: page size roundup should be done at VB2 core code, > for memory allocated there, and not at driver's level. Yet, looking at > VB2 code, it already does page size align at __setup_offsets(), but it > doesn't do if for the size field; just for the offset. > > The adjusted size should be stored at the VB2 size field, and the check for > buffer overflow, added on changeset 068a0df76023926af958a336a78bef60468d2033 > should be kept. > > IMO, it also makes sense to enforce that the USERPTR memory is multiple of the > page size, as otherwise the DMA transfer may overwrite some area that is > outside the allocated range. So, the size from USERPTR should be round down. > > That change, however, will break userspace, as it uses the picture sizeimage > to allocate the buffers. So, sizeimage needs to be PAGE_SIZE roundup before > passing it to userspace. > > Instead of modifying all drivers, the better seems to patch v4l_g_fmt() and > v4l_try_fmt() to return a roundup value for sizeimage. As usual, uvcvideo > requires a separate patch, because it doesn't use vidio_ioctl2. Hmm... PAGE_SIZE alignment is not needed on all places. It is needed only when DMA is done directly into the buffer, e. g. videobuf2-dma-contig and videobuf2-dma-sg. It means that we'll need an extra function for the VB2 memory allocation drivers to do do the memory-dependent roundups, and a new ancillary function at VB2 core for the VB2 clients to call to round sizeimage if needed. Regards, Mauro -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
