Re: [PATCH 2/2] virtio: let virtio use DMA API when guest RAM is protected
From: Halil Pasic
Date: Mon Feb 24 2020 - 14:00:40 EST
On Fri, 21 Feb 2020 17:36:45 +0100
Christoph Hellwig <hch@xxxxxx> 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