Re: [Xen-devel] [PATCH] fix XSA-46 regression with xend/xm

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 24/05/13 12:41, Gordan Bobic wrote:
> On Fri, 24 May 2013 12:19:32 +0100, George Dunlap 
> <George.Dunlap@xxxxxxxxxxxxx> wrote:
> > On Wed, May 22, 2013 at 9:51 PM, Gordan Bobic <gordan@xxxxxxxxxx> wrote:
> > > On 05/21/2013 09:56 AM, Ian Campbell wrote:
> > > > On Tue, 2013-05-21 at 09:40 +0100, Jan Beulich wrote:
> > > > > The hypervisor side changes for XSA-46 require the tool stack to now
> > > > > always map the guest pIRQ before granting access permission to the
> > > > > underlying host IRQ (GSI). This in particular requires that pciif.py
> > > > > no longer can skip this step (assuming qemu would do it) for HVM
> > > > > guests.
> > > > >
> > > > > This in turn exposes, however, an inconsistency between xend and 
> > > > > qemu:
> > > > > The former wants to always establish 1:1 mappings between pIRQ and 
> > > > > host
> > > > > IRQ (for non-MSI only of course), while the latter always wants to
> > > > > allocate an arbitrary mapping. Since the whole tool stack obviously
> > > > > should always agree on the mapping model, make libxc enforce the 1:1
> > > > > mapping as the more natural one (as well as being the one that allows
> > > > > for easier debugging, since there no need to find out the extra
> > > > > mapping). Users of libxc that want to establish a particular (rather
> > > > > than an allocated) mapping are still free to do so, as well as tool
> > > > > stacks not based on libxc wanting to implement an allocation based
> > > > > model (which is why it's not the hypervisor that's being changed to
> > > > > enforce either model).
> > > > >
> > > > > Since libxl, like xend, already uses a 1:1 model, it's unaffected by
> > > > > the libxc change (and it being unaffected by the original hypervisor
> > > > > side changes is - afaict - simply due to qemu getting spawned at a
> > > > > later point in time compared to the xend event flow).
> > > > >
> > > > > Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> > > > > Tested-by: Andreas Falck <falck.andreas.lists@xxxxxxxxx> (on 4.1)
> > > > > Tested-by: Gordan Bobic <gordan@xxxxxxxxxx> (on 4.2)
> > > >
> > > > In both cases tested with xend rather than xl or both?
> > >
> > > I can confirm that my VMs start fine with xl with this patch applied.
> > ...and they are HVM guests with devices passed through?
> Yes, HVM guests with PCI passthrough NIC, VGA passthrough, and USB
> passthrough.
Great, thanks!  I'll check this off my list.

 -George

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