On Thu, 2018-08-02 at 18:41 +0300, Michael S. Tsirkin wrote: > > > I don't completely agree: > > > > 1 - VIRTIO_F_IOMMU_PLATFORM is a property of the "other side", ie qemu > > for example. It indicates that the peer bypasses the normal platform > > iommu. The platform code in the guest has no real way to know that this > > is the case, this is a specific "feature" of the qemu implementation. > > > > 2 - VIRTIO_F_PLATFORM_DMA (or whatever you want to call it), is a > > property of the guest platform itself (not qemu), there's no way the > > "peer" can advertize it via the virtio negociated flags. At least for > > us. I don't know for sure whether that would be workable for the ARM > > case. In our case, qemu has no idea at VM creation time that the VM > > will turn itself into a secure VM and thus will require bounce > > buffering for IOs (including virtio). > > > > So unless we have another hook for the arch code to set > > VIRTIO_F_PLATFORM_DMA on selected (or all) virtio devices from the > > guest itself, I don't see that as a way to deal with it. > > > > > The other issue is VIRTIO_F_IO_BARRIER > > > which is very vaguely defined, and which needs a better definition. > > > And last but not least we'll need some text explaining the challenges > > > of hardware devices - I think VIRTIO_F_PLATFORM_DMA + VIRTIO_F_IO_BARRIER > > > is what would basically cover them, but a good description including > > > an explanation of why these matter. > > > > Ben. > > > > So is it true that from qemu point of view there is nothing special > going on? You pass in a PA, host writes there. Yes, qemu doesn't see a different. It's the guest that will bounce the pages via a pool of "insecure" pages that qemu can access. Normal pages in a secure VM come from PAs that qemu cannot physically access. Cheers, Ben. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
