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Re: [RFC 0/7] Proposal to make x86 IOMMU driver support configurable
- To: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>, Xenia Ragiadakou <burzalodowa@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 20 Dec 2022 11:09:33 +0100
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- Cc: Paul Durrant <paul@xxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Jun Nakajima <jun.nakajima@xxxxxxxxx>, Kevin Tian <kevin.tian@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 20 Dec 2022 10:09:42 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 19.12.2022 19:28, Andrew Cooper wrote:
> IOMMUs are more tricky still. They are (for most intents and purposes)
> mandatory on systems with >254 CPUs. We could in principle start
> supporting asymmetric IRQ routing on large systems, but Xen doesn't
> currently and it would be a lot work that's definitely not high on the
> priority list. At a minimum, this will need expressing in the Kconfig
> help text.
>
> We need to decide whether it is sensible to allow users to turn off
> IOMMU support. It probably is, because you could trivially do this by
> selecting CONFIG_INTEL only, and booting the result on an AMD system.
One other thing Andrew and I have been talking about: We probably do
not want to tie the IOMMU vendor control to CPU vendor one. IOW we'd
like to be able to e.g. build a hypervisor supporting Intel (only) as
the CPU vendor, but at the same time having support for an AMD IOMMU.
> For the names, I don't think AMD_IOMMU vs INTEL_VTD is a sensible.
> Probably wants to be INTEL_IOMMU to match.
Or simply VTD, covering the case than some other vendor comes up with a
clone. But of course we have that same issue with "AMD" and Hygon ...
Jan
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