On Sat, Sep 11, 2010 at 03:41:14PM +0800, Xin, Xiaohui wrote: > >>Playing with rlimit on data path, transparently to the application in this way > >>looks strange to me, I suspect this has unexpected security implications. > >>Further, applications may have other uses for locked memory > >>besides mpassthru - you should not just take it because it's there. > >> > >>Can we have an ioctl that lets userspace configure how much > >>memory to lock? This ioctl will decrement the rlimit and store > >>the data in the device structure so we can do accounting > >>internally. Put it back on close or on another ioctl. > >Yes, we can decrement the rlimit in ioctl in one time to avoid > >data path. > > > >>Need to be careful for when this operation gets called > >>again with 0 or another small value while we have locked memory - > >>maybe just fail with EBUSY? or wait until it gets unlocked? > >>Maybe 0 can be special-cased and deactivate zero-copy?. > >> > > How about we don't use a new ioctl, but just check the rlimit > in one MPASSTHRU_BINDDEV ioctl? If we find mp device > break the rlimit, then we fail the bind ioctl, and thus can't do > zero copy any more. Yes, and not just check, but decrement as well. I think we should give userspace control over how much memory we can lock and subtract from the rlimit. It's OK to add this as a parameter to MPASSTHRU_BINDDEV. Then increment the rlimit back on unbind and on close? This opens up an interesting condition: process 1 calls bind, process 2 calls unbind or close. This will increment rlimit for process 2. Not sure how to fix this properly. -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
