On Sun, Sep 19, 2010 at 06:28:19PM +0200, Avi Kivity wrote: > On machines without monitor/mwait we use an sti; hlt sequence to atomically > enable interrupts and put the cpu to sleep. The sequence uses the "interrupt > shadow" property of the sti instruction: interrupts are enabled only after > the instruction following sti has been executed. This means an interrupt > cannot happen in the middle of the sequence, which would leave us with > the interrupt processed but the cpu halted. > > The interrupt shadow, however, can be broken by an nmi; the following > sequence > > sti > nmi ... iret > # interrupt shadow disabled > intr ... iret > hlt > > puts the cpu to sleep, even though the interrupt may need additional > processing after the hlt (like scheduling a task). Doesn't the interrupt return path check for a re-schedule condition before iret? So to my believe the handler would not jump back to the idle task if something else becomes running in the interrupt handler, no? Joerg -- 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
