On 15.08.2012, at 20:16, Scott Wood wrote: > 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. Hrm. What happened to your patch that flushes the icache on cpu_physical_memory_rw? 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
