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Subject: Re: [PATCH 4/4] virtio-iommu: Clarify hot-unplug behavior
On Sat, Aug 12, 2023 at 03:25:10PM +0900, Akihiko Odaki wrote: > > > By the way, crosvm's logic to detach endpoint on removal looks incorrect for > > > me. A domain may have several endpoints attached, but the code looks like > > > it's always destroying a domain whether there are other endpoints attached > > > to the domain. I'm adding Zide Chen, who wrote the code according to git > > > blame, and crosvm-dev@chromium.org to CC. > > > > Link to this thread for more context: > > https://lore.kernel.org/virtio-dev/20230803153238.541803-5-jean-philippe@linaro.org/ > > > > I thought crosvm rejected attaching multiple endpoints to one domain but I > > think I misread. Rejecting multiple attach would be a straightforward fix > > (it's allowed by the spec), though it would prevent assigning endpoints > > that cannot be isolated from each others by the hardware (the driver won't > > attach those to different domains, if it's made aware that they should be > > in the same IOMMU group, for example if they are on a conventional PCI > > bus). > > Now we figured out an endpoint should not be detached from a domain without > a request from the driver anyway so the code to detach an endpoint can be > simply removed. Yes, but I think the other detach path, when handling ATTACH or DETACH requests, doesn't support domains with multiple endpoints attached either: // Currently, we only support detaching an endpoint if it is the only endpoint attached // to its domain. But the ATTACH handler seems to accept attaching multiple endpoints to the same domain? Thanks, Jean
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