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

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

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.


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