On 15.08.2012, at 19:26, Scott Wood wrote: > On 08/15/2012 04:52 AM, Alexander Graf wrote: >> >> On 15.08.2012, at 03:23, Scott Wood wrote: >> >>> On 08/14/2012 06:04 PM, Alexander Graf wrote: >>>> When we map a page that wasn't icache cleared before, do so when first >>>> mapping it in KVM using the same information bits as the Linux mapping >>>> logic. That way we are 100% sure that any page we map does not have stale >>>> entries in the icache. >>> >>> We're not really 100% sure of that -- this only handles the case where >>> the kernel does the dirtying, not when it's done by QEMU or the guest. >> >> When the guest does it, the guest is responsible for clearing the >> icache. Same for QEMU. It needs to clear it when doing DMA. > > Sure. I was just worried that that commit message could be taken the > wrong way, as in "we no longer need the QEMU icache flushing patch". > >> However, what is still broken would be a direct /dev/mem map. There >> QEMU should probably clear the icache before starting the guest, in >> case another guest was running on that same memory before. >> Fortunately, we don't have that mode available in upstream QEMU :). > > How is QEMU loading images different if it's /dev/mem versus ordinary > anonymous memory? You probably won't have stale icache data in the > latter case (which makes it less likely to be a problem in pratice), but > in theory you could have data that still hasn't left the dcache. It's the same. I just talked to Ben about this today in a different context and we should be safe :). 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
