On Tue, 14 Dec 2010 01:24:50 +0100 Alexander Graf <alex@xxxxxxxxx> wrote: > > On 14.12.2010, at 01:18, Scott Wood wrote: > > > Right, but I'm not talking about an interrupt that happens when the > > virtual EE bit is zero. I'm talking about an interrupt that happens > > right in the middle of the paravirt sequence -- after reading int_pending, > > but before setting critical to r2. > > > > It seems like the race window is just narrowed, not eliminated. > > Hrm, is that window really that important? There's usually plenty of interrupts and mmios coming through to always have some check going on. It could be important for realtime loads, tickless systems (especially if the Linux host eventually grows the ability to be tickless even when things are running), etc., and it makes me nervous in general. It's not something that's going to be causing problems all the time, though. > If it really is important, we could also check int_pending right after the critical section and just do a nop exit. Doesn't checking int_pending require clobbering registers, which is why we have the critical section in the first place? > That way we worst case waste a few cycles for the useless guest exit, > but always fetch interrupts immediately when they occur. What useless guest exit? Either we exit when we see an interrupt pending (in which case it's not useless), or we exit all the time, and then what's the point of the paravirt? -Scott -- To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
