Messages in this thread | | | Date | Mon, 24 Feb 2020 19:59:28 +0100 | From | Halil Pasic <> | Subject | Re: [PATCH 2/2] virtio: let virtio use DMA API when guest RAM is protected |
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On Fri, 21 Feb 2020 17:36:45 +0100 Christoph Hellwig <hch@lst.de> wrote:
> > By "legacy devices" I assume you mean pre-virtio-1.0 devices, that > > lack the F_VERSION_1 feature flag. Is that right? Because I don't > > see how being a legacy device or not relates to use of the DMA API. > > No. "legacy" is anything that does not set F_ACCESS_PLATFORM.
FYI in virtio-speak the term 'legacy devices' is already taken and it ain't congruent with your intended semantics. Please look it up https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/virtio-v1.1-cs01.html#x1-60001
But with that understood your statement does provide insisting in how do you see F_ACCESS_PLATFORM. I.e. something that should be enabled in general, except for legacy reasons. But I'm afraid Michael sees it differently: i.e. something that should be enabled when necessary, and otherwise not (because it is likely to cost performance).
Regards, Halil
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