RE: [Xen-devel] [PATCH][RFC] Support more Capability StructuresandDevice Specific

["Cui, Dexuan" <dexuan.cui@xxxxxxxxx>]

Hi Yuji,
I looked at the patch.  It seems pretty good. 
Except for the (temporary) absence of MSI/MSI-X stuff, looks the passthrough 
policy in the patch is almost the same as what is discussed in the PDF file 
Eddie posted.

I also made some tests against the patch, and found there may be some unstable 
issues:
I.e., when I boot a 32e RHEL5u1 (I add the "pci=nomsi" parameter)), it can 
easily (30%~80% probable) stay for a very long (i.e., >40s) at "Starting 
udev:", and after I login in shell, the NIC seems not present (the guest has no 
network available), but "lspci" shows the NIC is there.
If I use the Qemu without your patch, the issue disappears at once, and NIC in 
guest works well.

I haven't found issue in your patch yet. :)

Thanks,
-- Dexuan


-----Original Message-----
From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Yuji Shimada
Sent: 2008年6月30日 12:32
To: Ian Jackson
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx; Dong, Eddie; Keir Fraser
Subject: Re: [Xen-devel] [PATCH][RFC] Support more Capability 
StructuresandDevice Specific

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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