On Fri 18-10-13 14:59:17, Archit Taneja wrote: > Hi, > > On Friday 18 October 2013 03:46 AM, Jan Kara wrote: > > Hello, > > > > I was auditing get_user_pages() users and I've noticed that > >omap_vout_uservirt_to_phys() is apparently called for arbitrary address > >passed from userspace. If this address is in VM_IO vma, we use > >vma->vm_pgoff for mapping the virtual address to a physical address. > >However I don't think this is a generally valid computation for arbitrary > >VM_IO vma. So do we expect vma to come from a particular source where this > >is true? If yes, where do we expect vma comes from? Thanks for > >clarification. > > I don't know much about this domain, so I might be wrong here. > > The function omap_vout_uservirt_to_phys() is used in the mode > 'V4L2_MEMORY_USERPTR', to recieve a virtual address from the user. > > The driver hardware only works with physically contiguous buffers. > So I'm guessing this vma maps to a buffer mmaped by the user > application by some other device(like a camera or something). This > way, the user doesn't need to copy the buffer between the 2 devices. > I guess the computation works in that case. We don't have any safety > checks for this though. OK, so you really expect vma to be setup in a particular way. In videobuf2 framework this seems to correspond to what drivers/media/v4l2-core/videobuf2-vmalloc.c is doing (although that one is checking the range is really physically contiguous in vb2_get_contig_userptr()). > This driver is currenlty using the videobuf() framework, we would > eventually switch to videobuf2(), and hopefully this code shouldn't > even exist then. This is good to know but if that isn't happening soon I guess I'll convert the code somehow because I want to do some changes to the way get_user_pages() is called. Thanks for your explanation. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- 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
