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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.05.13 at 12:06, George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:
> 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.

Please do so then, because I had committed it already before you
even raised your concern (on the basis of it being a bug fix).

Jan


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