On Sat, 16 Mar 2013, Michel Lespinasse wrote: > On Sat, Mar 16, 2013 at 4:39 PM, Will Huck <will.huckk@xxxxxxxxx> wrote: > > On 03/15/2013 07:39 PM, Gil Weber wrote: > >> I am experiencing an issue with my device driver. I am using mmap and > >> ioctl to share information with my user space application. > >> The thing is that the shared memory does not seems to be synced. Do check > >> this, I have done a simple test: > > So if I got this right, the issue is that the vmalloc_area is > virtually aliased between the kernel and the user space mapping, so > that coherency is not guaranteed on architectures that use virtually > aliased caches. > > fs/aio.c does something similar to what you want with their ring > buffer. The kernel doesn't access the ring buffer through a vmalloc > area like you're trying to do; instead it uses kmap_atomic() .. > kunmap_atomic() whenever it wants to access it. > > I don't actually consider myself an expert in this area but I believe > the above should solve your problem :) I don't think so: kmap_atomic() provides a temporary kernel mapping for a page when not all memory is direct-mapped, but it's close to a no-op when there's no highmem. This question isn't about highmem. I can't point to what solves the problem for the aio ringbuffer: for all I know, that's not even used on such architectures. The usual solution is flush_dcache_page(): see Documentation/cachetlb.txt. Which mostly describes the common page cache case, but a driver like yours may also need it. Each architecture has its own implementation, and often its own way of minimizing the overhead of flush_dcache_page(): if you're using it in a new context, you might need to be careful about such optimizations, and the page flags used to control them. But better to ask on the (moderated) linux-arm-kernel list if it's not clear to you how to use it: being a no-op on x86, those of us who know little beyond x86 are apt to give bad advice. Hugh -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>