On Thu, Feb 20, 2020 at 05:17:48PM -0800, Ram Pai wrote: > On Thu, Feb 20, 2020 at 03:55:14PM -0500, Michael S. Tsirkin wrote: > > On Thu, Feb 20, 2020 at 05:06:06PM +0100, Halil Pasic wrote: > > > Currently the advanced guest memory protection technologies (AMD SEV, > > > powerpc secure guest technology and s390 Protected VMs) abuse the > > > VIRTIO_F_IOMMU_PLATFORM flag to make virtio core use the DMA API, which > > > is in turn necessary, to make IO work with guest memory protection. > > > > > > But VIRTIO_F_IOMMU_PLATFORM a.k.a. VIRTIO_F_ACCESS_PLATFORM is really a > > > different beast: with virtio devices whose implementation runs on an SMP > > > CPU we are still fine with doing all the usual optimizations, it is just > > > that we need to make sure that the memory protection mechanism does not > > > get in the way. The VIRTIO_F_ACCESS_PLATFORM mandates more work on the > > > side of the guest (and possibly he host side as well) than we actually > > > need. > > > > > > An additional benefit of teaching the guest to make the right decision > > > (and use DMA API) on it's own is: removing the need, to mandate special > > > VM configuration for guests that may run with protection. This is > > > especially interesting for s390 as VIRTIO_F_IOMMU_PLATFORM pushes all > > > the virtio control structures into the first 2G of guest memory: > > > something we don't necessarily want to do per-default. > > > > > > Signed-off-by: Halil Pasic <pasic@xxxxxxxxxxxxx> > > > Tested-by: Ram Pai <linuxram@xxxxxxxxxx> > > > Tested-by: Michael Mueller <mimu@xxxxxxxxxxxxx> > > > > This might work for you but it's fragile, since without > > VIRTIO_F_ACCESS_PLATFORM hypervisor assumes it gets > > GPA's, not DMA addresses. > > > > > > > > IOW this looks like another iteration of: > > > > virtio: Support encrypted memory on powerpc secure guests > > > > which I was under the impression was abandoned as unnecessary. > > It has been abondoned on powerpc. We enabled VIRTIO_F_ACCESS_PLATFORM; > by default, flag on powerpc. Uh... we haven't yet, though we're working on it. > We would like to enable secure guests on powerpc without this flag > aswell enabled, but past experience has educated us that its not a easy > path. However if Halil makes some inroads in this path for s390, we > will like to support him. > > > RP > -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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