Re: [Xen-devel] iommu=dom0-passthrough behavior

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.11.12 at 09:23, "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx> wrote:

> 
>> -----Original Message-----
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: Wednesday, November 14, 2012 9:40 PM
>> To: Zhang, Xiantao; Zhang, Yang Z
>> Cc: wei.huang2@xxxxxxx; weiwang.dd@xxxxxxxxx; xen-devel
>> Subject: RE: [Xen-devel] iommu=dom0-passthrough behavior
>> 
>> >>> On 14.11.12 at 01:37, "Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>
>> wrote:
>> >> >> c) we could provide a command line option to allow fake devices to
>> >> >>     be create
>> >> >
>> >> > Agree, this maybe a feasible solution I can figure out, so far.
>> >> >
>> >> >> d) we could create context entries for all BDFs, whether or not a
>> >> >>     device exists there
>> >> >
>> >> > As I said,  this maybe bring security issue. Even for the
>> >> > iommu-passthrough option,  it is also not suggested to be used if
>> >> > security
>> > is
>> >> considered.
>> >>
>> >> As said - it is clear that the basic thing here (using
>> >> "iommu=dom0-passthrough") is already weakening security. So security
>> >> isn't the concern in this discussion, that's left to whoever is
>> >> intending to use
>> > that
>> >> option.
>> >
>> > Okay,  I vote your option C if don't care security.
>> 
>> Which, if I'm not mistaken, could be implemented entirely independent of
>> "iommu=dom0-passthrough". I'll see if that helps on the offending system.
> 
> I mean this one: 
>>>c) we could provide a command line option to allow fake devices to be create
> 
> Yes,  I don't think "iommu=dom0-passthrough" can meet your requirement.
>  We had better add a cmd line option to  pass the related information to 
> hypervisor and VT-d can create 
> the pass-through context entry  for the undetectable device.  

You misunderstood: What I was saying (and seeking confirmation)
is that I don't think the new command line option would need to
have any connection to the existing, non-suitable one. In
particular, for it to take effect, "iommu=dom0-passthrough"
wouldn't need to be specified at all.

Jan


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