On Wed, 2010-11-03 at 12:48 +0200, Michael S. Tsirkin wrote: > I mean in practice, you see a benefit from this patch? Yes, I tested it. It does benefit the performance. > > My concern here is whether checking only in set up would be > sufficient > > for security? > > It better be sufficient because the checks that put_user does > are not effictive when run from the kernel thread, anyway. > > > Would be there is a case guest could corrupt the ring > > later? If not, that's OK. > > You mean change the pointer after it's checked? > If you see such a case, please holler. I wonder about it, not a such case in mind. > To clarify: the combination of __put_user and separate > signalling is giving the same performance benefit as your > patch? Yes, it has similar performance, not I haven't finished all message sizes comparison yet. > I am mostly concerned with adding code that seems to help > speed for reasons we don't completely understand, because > then we might break the optimization easily without noticing. I don't think the patch I submited would break up anything. It just reduced the cost of per used buffer 3 put_user() calls and guest signaling from one to one to many to one. Thanks Shirley -- 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
