Re: [PATCH v4 1/2] iommu/sva: Tighten SVA bind API with explicit flags

[Jason Gunthorpe]

On Tue, May 11, 2021 at 09:14:52AM -0700, Jacob Pan wrote:

> > Honestly, I'm not convinced we should have "kernel SVA" at all.. Why
> > does IDXD use normal DMA on the RID for kernel controlled accesses?
> 
> Using SVA simplifies the work submission, there is no need to do map/unmap.
> Just bind PASID with init_mm, then submit work directly either with ENQCMDS
> (supervisor version of ENQCMD) to a shared workqueue or put the supervisor
> PASID in the descriptor for dedicated workqueue.

That is not OK, protable drivers in Linux have to sue dma map/unmap
calls to manage cache coherence. PASID does not opt out of any of
that.

I dislike this whole idea a lot. A single driver should not opt itself
out of IOMMU based security "just because"

Jason