On 04/01/2014 09:03 PM, John Stultz wrote: > > So, maybe its best to ignore the fact that folks want to do semi-crazy > user-space faulting via SIGBUS. At least to start with. Lets look at the > semantic for the "normal" mark volatile, never touch the pages until you > mark non-volatile - basically where accessing volatile pages is similar > to a use-after-free bug. > > So, for the most part, I'd say the proposed SIGBUS semantics don't > complicate things for this basic use-case, at least when compared with > things like zero-fill. If an applications accidentally accessed a > purged volatile page, I think SIGBUS is the right thing to do. They most > likely immediately crash, but its better then them moving along with > silent corruption because they're mucking with zero-filled pages. > > So between zero-fill and SIGBUS, I think SIGBUS makes the most sense. If > you have a third option you're thinking of, I'd of course be interested > in hearing it. > People already do SIGBUS for mmap, so there is nothing new here. > Now... once you've chosen SIGBUS semantics, there will be folks who will > try to exploit the fact that we get SIGBUS on purged page access (at > least on the user-space side) and will try to access pages that are > volatile until they are purged and try to then handle the SIGBUS to fix > things up. Those folks exploiting that will have to be particularly > careful not to pass volatile data to the kernel, and if they do they'll > have to be smart enough to handle the EFAULT, etc. That's really all > their problem, because they're being clever. :) Yep. -hpa -- 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>