Re: [Xen-devel] [v2][PATCH] xen/vtd/iommu: permit group devices to passthrough in relaxed mode

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.09.15 at 01:22, <kevin.tian@xxxxxxxxx> wrote:
> Sorry it's a bad example. My actual concern is that we can't count
> on this per-VM relax/strict policy to prevent group devices assigned
> to different VM. In that case it's definitely a security hole since
> one VM may clobber shared RMRR to impact another VM. So right
> example for that scenario is both VMs specified with 'relax'. 

Sorry, no, the idea of "relax" is to allow the admin to state "I have
no security concerns". Hence we'd have a security issue only if the
default was "relax" (which iiuc it isn't, or if it were _that's_ what
would need to be alongside the presented change). Whether that
statement of the admin is because of
- knowing that the RMRR won't be used post-boot
- group-assigning the devices manually
- simply not caring (i.e. trusting the guests)
is not our business.

IOW, provided there's no way for "relax" to become the default
(Tiejun - please confirm), the patch as is should be fine.

Jan



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