On Mon, Mar 19, 2007 at 09:44:28PM +0100, Blaisorblade wrote: > On Sunday 18 March 2007 03:50, Nick Piggin wrote: > > > > > > > > Yes, I believe that is the case, however I wonder if that is going to > > > > be a problem for you to distinguish between write faults for clean > > > > writable ptes, and write faults for readonly ptes? > > > > > > I wouldn't be able to distinguish them, but am I going to get write > > > faults for clean ptes when vma_wants_writenotify() is false (as seems to > > > be for tmpfs)? I guess not. > > > > > > For tmpfs pages, clean writable PTEs are mapped as writable so they won't > > > give any problem, since vma_wants_writenotify() is false for tmpfs. > > > Correct? > > > > Yes, that should be the case. So would this mean that nonlinear protections > > don't work on regular files? > > They still work in most cases (including for UML), but if the initial mmap() > specified PROT_WRITE, that is ignored, for pages which are not remapped via > remap_file_pages(). UML uses PROT_NONE for the initial mmap, so that's no > problem.
But how are you going to distinguish a write fault on a readonly pte for dirty page accounting vs a read-only nonlinear protection? You can't store any more data in a present pte AFAIK, so you'd have to have some out of band data. At which point, you may as well just forget about vma_wants_writenotify vmas, considering that everybody is using shmem/ramfs. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
