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

[Gordan Bobic <gordan@bobich.net>]

 On Fri, 24 May 2013 12:19:32 +0100, George Dunlap 
 <George.Dunlap@eu.citrix.com> wrote:
> On Wed, May 22, 2013 at 9:51 PM, Gordan Bobic <gordan@bobich.net> 
> 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@suse.com>
>>>> Tested-by: Andreas Falck <falck.andreas.lists@gmail.com> (on 4.1)
>>>> Tested-by: Gordan Bobic <gordan@bobich.net> (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.

 Gordan