On Tue, Jun 16, 2020 at 12:09:16PM -0400, Peter Xu wrote:
> On Tue, Jun 16, 2020 at 04:49:28PM +0100, Stefan Hajnoczi wrote:
> > Isolation between applications is preserved but there is no isolation
> > between the device and the application itself. The application needs to
> > trust the device.
> > 
> > Examples:
> > 
> > 1. The device can snoop secret data from readable pages in the
> >    application's virtual memory space.
> > 
> > 2. The device can gain arbitrary execution on the CPU by overwriting
> >    control flow addresses (e.g. function pointers, stack return
> >    addresses) in writable pages.
> 
> To me, SVA seems to be that "middle layer" of secure where it's not as safe as
> VFIO_IOMMU_MAP_DMA which has buffer level granularity of control (but of course
> we pay overhead on buffer setups and on-the-fly translations), however it's far
> better than DMA with no IOMMU which can ruin the whole host/guest, because
> after all we do a lot of isolations as process based.
> 
> IMHO it's the same as when we see a VM (or the QEMU process) as a whole along
> with the guest code.  In some cases we don't care if the guest did some bad
> things to mess up with its own QEMU process.  It is still ideal if we can even
> stop the guest from doing so, but when it's not easy to do it the ideal way, we
> just lower the requirement to not spread the influence to the host and other
> VMs.

Makes sense.

Stefan