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

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 05/21/2013 10:56 AM, Jan Beulich wrote:
> > > > On 21.05.13 at 11:44, George Dunlap <George.Dunlap@xxxxxxxxxxxxx> wrote:
> > On Tue, May 21, 2013 at 9:40 AM, Jan Beulich <JBeulich@xxxxxxxx> 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)
> > I think to get a release ack, someone will need to commit to testing
> > it with xl for 4.3.
> It is pretty obvious (see the description) that xl is unaffected.
It's pretty obvious that you think so, but it's my job to be skeptical. 
:-)  If both xend and xl assume a 1:1 model, and this patch changes 
things for xend, why is it not possible for this to have an effect on 
xl?  You have a guess, but it's marked "afaict".
In any case it should be pretty straightforward to have done.  We could 
even check it in and just put a release blocker, "Someone tests 
pass-through with xl" to make sure we don't forget it.
 -George

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