On 21/08/19 07:03, Peter Xu wrote: > On Tue, Aug 20, 2019 at 08:24:49AM +0200, Paolo Bonzini wrote: >> On 20/08/19 07:22, Peter Xu wrote: >>> On Mon, Aug 12, 2019 at 09:45:27AM +0200, Peter Xu wrote: >>>> This is a RFC series. >>>> >>>> The VT-d code has some defects, one of them is that we cannot detect >>>> the misuse of vIOMMU and vfio-pci early enough. >>>> >>>> For example, logically this is not allowed: >>>> >>>> -device intel-iommu,caching-mode=off \ >>>> -device vfio-pci,host=05:00.0 >>>> >>>> Because the caching mode is required to make vfio-pci devices >>>> functional. >>>> >>>> Previously we did this sanity check in vtd_iommu_notify_flag_changed() >>>> as when the memory regions change their attributes. However that's >>>> too late in most cases! Because the memory region layouts will only >>>> change after IOMMU is enabled, and that's in most cases during the >>>> guest OS boots. So when the configuration is wrong, we will only bail >>>> out during the guest boots rather than simply telling the user before >>>> QEMU starts. >>>> >>>> The same problem happens on device hotplug, say, when we have this: >>>> >>>> -device intel-iommu,caching-mode=off >>>> >>>> Then we do something like: >>>> >>>> (HMP) device_add vfio-pci,host=05:00.0,bus=pcie.1 >>>> >>>> If at that time the vIOMMU is enabled in the guest then the QEMU >>>> process will simply quit directly due to this hotplug event. This is >>>> a bit insane... >>>> >>>> This series tries to solve above two problems by introducing two >>>> sanity checks upon these places separately: >>>> >>>> - machine done >>>> - hotplug device >>>> >>>> This is a bit awkward but I hope this could be better than before. >>>> There is of course other solutions like hard-code the check into >>>> vfio-pci but I feel it even more unpretty. I didn't think out any >>>> better way to do this, if there is please kindly shout out. >>>> >>>> Please have a look to see whether this would be acceptable, thanks. >>> >>> Any more comment on this? >> >> No problem from me, but I wouldn't mind if someone else merged it. :) > > Can I read this as an "acked-by"? :)
Yes, it shouldn't even need Acked-by since there are other maintainers that handle this part of the tree: Paolo Bonzini <pbonz...@redhat.com> (maintainer:X86 TCG CPUs) Richard Henderson <r...@twiddle.net> (maintainer:X86 TCG CPUs) Eduardo Habkost <ehabk...@redhat.com> (maintainer:X86 TCG CPUs) "Michael S. Tsirkin" <m...@redhat.com> (supporter:PC) Marcel Apfelbaum <marcel.apfelb...@gmail.com> (supporter:PC) > Michael, should this be for your tree? What do you think about the > series? Please let me know what I need to do to move this forward. I > can repost a non-rfc series if needed, but it'll be exactly the same > content. > > Regards, >