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

[George Dunlap <george.dunlap@eu.citrix.com>]

On 05/21/2013 10:56 AM, Jan Beulich wrote:
>>>> On 21.05.13 at 11:44, George Dunlap <George.Dunlap@eu.citrix.com> wrote:
>> On Tue, May 21, 2013 at 9:40 AM, Jan Beulich <JBeulich@suse.com> 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@suse.com>
>>> Tested-by: Andreas Falck <falck.andreas.lists@gmail.com> (on 4.1)
>>> Tested-by: Gordan Bobic <gordan@bobich.net> (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