On 15.08.2012, at 20:33, Scott Wood wrote: > On 08/15/2012 01:29 PM, Alexander Graf wrote: >> >> On 15.08.2012, at 20:27, Alexander Graf wrote: >> >>> >>> 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? > > IIRC Ben wanted it conditionalized to not slow things down on > icache-coherent systems, and I never got around to respinning it. No, he was saying that DMA doesn't flush the icache: http://thread.gmane.org/gmane.comp.emulators.qemu/119022/focus=119086 > >> Ah, if I read Ben's comment correctly we only need it for rom loads, not always for cpu_physical_memory_rw. > > Why? Because guest Linux apparently assumes that DMA'd memory needs to be icache flushed. 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
