Re: [Xen-devel] [PATCH] PCI/MSI: don't disable AMD IOMMU MSI on Xen dom0

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.06.12 at 14:28, Wei Wang <wei.wang2@xxxxxxx> wrote:
> On 06/21/2012 02:06 PM, Jan Beulich wrote:
>>>>> On 21.06.12 at 13:21, Wei Wang<wei.wang2@xxxxxxx>  wrote:
>>> I also evaluated the possibility of hiding iommu device from dom0. I
>>> think the change is no quite a lot, at least, for io based pcicfg
>>> access. A proof-of-concept patch is attached.
>>
>> This completely hides the device from Dom0, but only when
>> config space is accessed via method 1. Did you not see my
>> earlier patch doing this for MCFG as well
> Could you please provide a particular c/s number?... (I saw too many c/s 
> might be related to this topic). so that I could work out a patch to 
> support both i/o and mmcfg.

I sent this to you yesterday, so you'd be able to test whether
it actually fulfills its purpose before we discuss whether this is
acceptable for 4.2. See
http://lists.xen.org/archives/html/xen-devel/2012-06/msg01129.html

> (albeit only disallowing
>> writes, so allowing the device to still be seen by Dom0)?
> Sounds better to me...this still allows user to check iommu status from 
> lspci.
> 
>> Whether completely hiding the device is actually okay I can't
>> easily tell: Would IOMMUs always be either at func 0 of a single-
>> unction device, or at a non-zero func of a multi-function one? If
>> not, other devices may get hidden implicitly.
> 
> AMD IOMMU is an independent pci-e endpoint, and this function will not 
> be used for other purposes other than containing an iommu. So I don't 
> see that iommu will share bdf value with other devices.

The question is not regarding bdf, but regarding whether under
the same seg:bus:dev there might be multiple functions, one of
which is the IOMMU, and if so, whether the IOMMU would be
guaranteed to have a non-zero function number.

Jan


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