On 07/25/2014 04:10 PM, Peter Zijlstra wrote: > On Tue, Jul 22, 2014 at 04:09:59PM +0800, Yan, Zheng wrote: >> One corner case needs to mention is that the PEBS hardware doesn't >> deal well with collisions, when PEBS events happen near to each >> other. The records for the events can be collapsed into a single >> one. However in practice collisions are extremely rare, as long as >> different events are used. The periods are typically very large, >> so any collision is unlikely. When collision happens, we can either >> drop the PEBS record or use the record to serve multiple events. >> This patch chooses the later approach. > > You can't.. the events might have different security context. > > Remember, the overflow bit is set from the overflow until the PEBS > event is generated, this is quite a long time. So if another PEBS event > gets generated while the other is still pending it will have both bits > set. Even though the second bit is for another (unrelated) counter. > > The unrelated counter might not have privilege to observe the data of > the generated event. > > I think you can unwind and fully correct this trainwreck.
could you give more information how to do this. Regards Yan, Zheng > But simply > delivering an even with multiple bits set to all relevant events is > wrong and might leak sensitive information. > -- 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/
