Re: [Qemu-devel] [PATCH RFC 0/4] intel_iommu: Do sanity check of vfio-pci earlier

[Peter Xu]

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"? :)

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,

-- 
Peter Xu