On Fri, 3 May 2019 11:55:11 +0200 Cornelia Huck <cohuck@xxxxxxxxxx> wrote: > On Fri, 26 Apr 2019 20:32:35 +0200 > Halil Pasic <pasic@xxxxxxxxxxxxx> wrote: > > > Enhanced virtualization protection technology may require the use of > > bounce buffers for I/O. While support for this was built into the virtio > > core, virtio-ccw wasn't changed accordingly. > > > > Some background on technology (not part of this series) and the > > terminology used. > > > > * Protected Virtualization (PV): > > > > Protected Virtualization guarantees, that non-shared memory of a guest > > that operates in PV mode private to that guest. I.e. any attempts by the > > hypervisor or other guests to access it will result in an exception. If > > supported by the environment (machine, KVM, guest VM) a guest can decide > > to change into PV mode by doing the appropriate ultravisor calls. Unlike > > some other enhanced virtualization protection technology, > > I think that sentence misses its second part? > I wanted to kill the whole sentence, but killed only a part of it. :( Sorry. If any, the sentence had only significance for judging how well inherited some names fit. > > > > * Ultravisor: > > > > A hardware/firmware entity that manages PV guests, and polices access to > > their memory. A PV guest prospect needs to interact with the ultravisor, > > to enter PV mode, and potentially to share pages (for I/O which should > > be encrypted by the guest). A guest interacts with the ultravisor via so > > called ultravisor calls. A hypervisor needs to interact with the > > ultravisor to facilitate interpretation, emulation and swapping. A > > hypervisor interacts with the ultravisor via ultravisor calls and via > > the SIE state description. Generally the ultravisor sanitizes hypervisor > > inputs so that the guest can not be corrupted (except for denial of > > service. > > > > > > What needs to be done > > ===================== > > > > Thus what needs to be done to bring virtio-ccw up to speed with respect > > to protected virtualization is: > > * use some 'new' common virtio stuff > > Doing this makes sense regardless of the protected virtualization use > case, and I think we should go ahead and merge those patches for 5.2. > I agree. > > * make sure that virtio-ccw specific stuff uses shared memory when > > talking to the hypervisor (except control/communication blocks like ORB, > > these are handled by the ultravisor) > > TBH, I'm still a bit hazy on what needs to use shared memory and what > doesn't. > It is all in the code :). To have complete and definitive answers here we would need some sort of public UV architecture. > > * make sure the DMA API does what is necessary to talk through shared > > memory if we are a protected virtualization guest. > > * make sure the common IO layer plays along as well (airqs, sense). > > > > > > Important notes > > ================ > > > > * This patch set is based on Martins features branch > > (git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git branch > > 'features'). > > > > * Documentation is still very sketchy. I'm committed to improving this, > > but I'm currently hampered by some dependencies currently. > > I understand, but I think this really needs more doc; also for people > who want to understand the code in the future. > > Unfortunately lack of doc also hampers others in reviewing this :/ > I'm not sure how much can we do on the doc front. Without a complete architecture, one basically needs to trust the guys with access to the architecture. Many thanks for your feedback. Regards, Halil [..]
