Re: [RFC PATCH 0/7] Untrusted device support for virtio

[Michael S. Tsirkin]

On Thu, Apr 22, 2021 at 04:19:16PM +0800, Jason Wang wrote:
> 
> 在 2021/4/22 下午2:31, Christoph Hellwig 写道:
> > On Wed, Apr 21, 2021 at 11:21:10AM +0800, Jason Wang wrote:
> > > The behaivor for non DMA API is kept for minimizing the performance
> > > impact.
> > NAK.  Everyone should be using the DMA API in a modern world.  So
> > treating the DMA API path worse than the broken legacy path does not
> > make any sense whatsoever.
> 
> 
> I think the goal is not treat DMA API path worse than legacy. The issue is
> that the management layer should guarantee that ACCESS_PLATFORM is set so
> DMA API is guaranteed to be used by the driver. So I'm not sure how much
> value we can gain from trying to 'fix' the legacy path. But I can change the
> behavior of legacy path to match DMA API path.
> 
> Thanks

I think before we maintain different paths with/without ACCESS_PLATFORM
it's worth checking whether it's even a net gain. Avoiding sharing
by storing data in private memory can actually turn out to be
a net gain even without DMA API.

It is worth checking what is the performance effect of this patch.


-- 
MST