Re: [Xen-devel] Other PCI devices to mark mark as read-only for dom0

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.06.12 at 11:04, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> Following Jan's infrastructure to mark certain PCI devices as read only,
> I think it wise to now consider what other PCI devices should really be
> read only to dom0.
> 
> My preliminary thoughts include:
> 
> * PCI serial devices which Xen is configured to use

But only if they're single-function.

> * Chipset devices (AMD IOMMU covered by previous patch)
> * Cpu information

What are you thinking of here specifically.

> Are there any others I have overlooked, or reasons that dom0 should be
> able to write to these areas?
> 
> On a related note, should there be a mechanism for dom0 to determine
> which PCI configuration areas are read only to itself?

Perhaps, but that's not the only thing to deal with here. As
said previously, when we want to add devices with active BARs
here (luckily Wei confirmed that AMD IOMMUs have none),
Dom0 trying to re-configure them would get us into problems.
The issue exists today, but could become worse when we
disallow the updates (as that could lead to two devices sharing
resources they shouldn't share, whereas today a device in use
by Xen and getting re-assigned its resources would merely stop
working).

Jan


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