Re: [Xen-devel] [PATCH][RFC] Support more Capability Structures andDevice Specific

[Yuji Shimada <shimada-yxb@xxxxxxxxxxxxxxx>]

I think it is NOT safe to pass through operations with unknown
behaviour. qemu-dm should prevent guest software setting unsafe value
to register.  We have to investigate each register and decide to
emulate(virtualize) or passthrough.

I haven't investigated some capability structures (like PCI-X
Capability Structure).  I hide them from guest software.

Device Specific Registers (exclude capability structures) is
passthrough. In non-virtualized environment, OS does not touch device
specific registers, but device drivers configure them. In virtualized
environment, we have to allow device drivers to configure them.

--
Yuji Shimada

On Fri, 27 Jun 2008 14:34:11 +0100
Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx> wrote:

> Dong, Eddie writes ("RE: [Xen-devel] [PATCH][RFC] Support more Capability 
> Structures andDevice Specific"):
> > If we agree the basic policy is pass through except the ones with known
> > behavior, I think we don't need that many case to case handle. Dexuan is
> > working on the implementation base on the summit talk and close to end,
> > maybe Yuji and Dexuan can coordinate first to see if the proposed policy
> > can server yuji's purpose.
> 
> Is it really safe to pass through operations with unknown behavious ?
> Particularly if the system has an iommu, the administrator may be
> expecting the passthrough mechanism to defend the host from rogue
> behaviour by the card and its owning guest.
> 
> (I'm no expert on PCI so forgive me if this question is stupid.)
> 
> Ian.
> 
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