On Thu, Aug 25, 2011 at 08:25:45AM -0500, Alexander Graf wrote: > > On 25.08.2011, at 07:31, Roedel, Joerg wrote: > > > On Wed, Aug 24, 2011 at 11:07:46AM -0400, Alex Williamson wrote: > >> On Wed, 2011-08-24 at 10:52 +0200, Roedel, Joerg wrote: > > > > [...] > > >> We need to try the polite method of attempting to hot unplug the device > >> from qemu first, which the current vfio code already implements. We can > >> then escalate if it doesn't respond. The current code calls abort in > >> qemu if the guest doesn't respond, but I agree we should also be > >> enforcing this at the kernel interface. I think the problem with the > >> hard-unplug is that we don't have a good revoke mechanism for the mmio > >> mmaps. > > > > For mmio we could stop the guest and replace the mmio region with a > > region that is filled with 0xff, no? > > Sure, but that happens in user space. The question is how does > kernel space enforce an MMIO region to not be mapped after the > hotplug event occured? Keep in mind that user space is pretty much > untrusted here - it doesn't have to be QEMU. It could just as well > be a generic user space driver. And that can just ignore hotplug > events. We're saying you hard yank the mapping from the userspace process. That is, you invalidate all its PTEs mapping the MMIO space, and don't let it fault them back in. As I see it there are two options: (a) make subsequent accesses from userspace or the guest result in either a SIGBUS that userspace must either deal with or die, or (b) replace the mapping with a dummy RO mapping containing 0xff, with any trapped writes emulated as nops. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
