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

[Wei Wang <wei.wang2@xxxxxxx>]

On 06/21/2012 02:45 PM, Jan Beulich wrote:
> > > > 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
Oh, yes I found it, my email filter did not work well so I did not see 
it at the right folder. I will test right now.
> > (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.
In a real system (single or multiple iommu), amd iommu shares the same 
device number with north bridge but has function number 2.. (e.g 
bus:00.2) Howerver according to spec, it does not guaranteed to have 
non-zero function number. So what is the problem you see if iommu uses 
fun0 on a multi-func device?
Thanks,
Wei

> Jan


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