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. -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
