On Tuesday 20 March 2007 07:00, Nick Piggin wrote: > 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? Hmm... I was only thinking to PTEs which hadn't been remapped via remap_file_pages, but just faulted in with initial mmap() protection. For the other PTEs, however, I overlooked that the current code ignores vma_wants_writenotify(), i.e. breaks dirty page accounting for them, and I refused to even consider this opportunity, even without knowing the purposes of dirty pages accounting (I found the commits explaining this however). > 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. I was going to do that anyway. I'd guess that I should just disallow in remap_file_pages() the VM_MANYPROTS (i.e. MAP_CHGPROT in flags) && vma_wants_writenotify() combination, right? Ok, trivial (shouldn't even have pointed this out). -- Inform me of my mistakes, so I can add them to my list! Paolo Giarrusso, aka Blaisorblade http://www.user-mode-linux.org/~blaisorblade Chiacchiera con i tuoi amici in tempo reale! http://it.yahoo.com/mail_it/foot/*http://it.messenger.yahoo.com - 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/