On 27.09.2010, at 10:38, Avi Kivity wrote: > On 09/19/2010 06:28 PM, 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). >> >> sti is explicitly documented not to force an interrupt shadow; though many >> processors do inhibit nmi immediately after sti. >> >> Avoid the race by checking, during an nmi, if we hit the safe halt sequence. >> If we did, increment the instruction pointer past the hlt instruction; this >> allows an immediately following interrupt to return to a safe place. >> >> Signed-off-by: Avi Kivity<avi@xxxxxxxxxx> > > Ping. Wow, this is incredibly ugly :). Can't we just mask NMIs when the interrupt shadow is active? Alex -- 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
