On 08/15/2012 01:01 PM, Alexander Graf wrote: > > On 15.08.2012, at 19:47, Scott Wood wrote: > >> On 08/15/2012 12:27 PM, Alexander Graf wrote: >>> >>> 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 :). >> >> Safe how? >> >> If it's truly the same, we're definitely not safe, since I had problems >> with this using /dev/mem (particularly when changing the kernel image >> without a host reboot) before I put in the icache flush patch. > > QEMU needs to icache flush everything it puts into guest memory. Yes. I thought you meant we should be safe as things are now. -Scott -- 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
