Re: FreeBSD guest with VTD NIC not passing traffic

[Alex Williamson <alex.williamson@redhat.com>]

On Fri, 2012-01-13 at 22:33 +0100, Jan Kiszka wrote:
> On 2012-01-13 22:05, Alex Williamson wrote:
> > On Fri, 2012-01-13 at 22:00 +0100, Jan Kiszka wrote:
> >> On 2012-01-04 04:21, Alex Williamson wrote:
> >>> On Mon, 2011-12-19 at 19:49 +0530, Shashidhar Patil wrote:
> >>>> Hi,
> >>>>        I am running Ubuntu 10.10 (amd64) on a 2 socket  nehalem based
> >>>> server with IOH 5520. 5520 supports VTD.
> >>>> I enabled DMAR with intel_iommu=on. The box has intel 82599 adapter
> >>>> which I assigned through VT-D to FreeBSD 8.2 running
> >>>> as guest os. The ixgbe driver detects the device and the driver
> >>>> successfully configures the device. But the link
> >>>> never comes up. It looks like link up/down interrupts are not
> >>>> delivered. Then I checked kvm interrupt assignment and as expected
> >>>> kvm could not make MSI-X entries for the VT-d guest. So no output from
> >>>> "grep kvm /proc/interrupt". By enabling some debugs in the
> >>>> qemu-kvm I figured out that the MSI-x updates are not received
> >>>> properly. It does look like Linux updates MSI-X table in a batch
> >>>> fashion
> >>>> which qemu-kvm gets in  one shot and every thing works fine in case of
> >>>> linux. In case of FreeBSD PCIE updates come /MSI-X entry
> >>>> which qemu-kvm can't make use.
> >>>
> >>> That's right, Linux and Windows both seem to setup the MSI-X table then
> >>> enable it in one shot, so we only trigger the interrupt programming when
> >>> the enable bit is set.  We don't trigger changes on writes to the MSI-X
> >>> table... not very accurate emulation of mask bits.
> >>
> >> According to the PCI spec, updates that happen while a vector is
> >> unmasked, need not be considered by the hardware (thus the hypervisor
> >> here). Is that the scenario here?
> > 
> > I'm assuming the vector is masked in the MSI-X table.  So Linux/Windows
> > do:
> > 
> > a) program MSI-X table
> > b) enable MSI-X in capability register
> > 
> > Whereas FreeBSD does:
> > 
> > a) enable MSI-X in capability register (vectors masked in table)
> > b) program and unmask individual vectors
> 
> That should work with the current code. It checks the number of vectors
> on each config write, iterates the whole table, and then updates the
  ^^^^^^^^^^^^^^^^^^^^
> kernel configuration accordingly. It even requires the enable bit in the
> cap register to be set before doing this.

That's the problem, we only do it on config writes overlapping the MSI-X
flags.  We don't do anything for writes to the MSI-X table.  It might be
as simple as calling assigned_dev_update_msix() from msix_mmio_writel()
when the mask bit is toggled.  I'm not sure what might fall out of that
though.  Thanks,

Alex