Re: [PATCH 00/10] s390: virtio: support protected virtualization

Cornelia Huck
2019-05-03T09:55:11Z

On Fri, 26 Apr 2019 20:32:35 +0200
Halil Pasic <pasic@linux.ibm.com> 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?

>
> * 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.

> * 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.

> * 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 :/

>
> * The existing naming in the common infrastructure (kernel internal
> interfaces) is pretty much based on the AMD SEV terminology. Thus the
> names aren't always perfect. There might be merit to changing these
> names to more abstract ones. I did not put much thought into that at
> the current stage.
>
> * Testing: Please use iommu_platform=on for any virtio devices you are
> going to test this code with (so virtio actually uses the DMA API).
>
> Change log
> ==========
>
> RFC --> v1:
> * Fixed bugs found by Connie (may_reduce and handling reduced, warning,
> split move -- thanks Connie!).
> * Fixed console bug found by Sebastian (thanks Sebastian!).
> * Removed the completely useless duplicate of dma-mapping.h spotted by
> Christoph (thanks Christoph!).
> * Don't use the global DMA pool for subchannel and ccw device
> owned memory as requested by Sebastian. Consequences:
> * Both subchannel and ccw devices have their dma masks
> now (both specifying 31 bit addressable)
> * We require at least 2 DMA pages per ccw device now, most of
> this memory is wasted though.
> * DMA memory allocated by virtio is also 31 bit addressable now
> as virtio uses the parent (which is the ccw device).
> * Enabled packed ring.
> * Rebased onto Martins feature branch; using the actual uv (ultravisor)
> interface instead of TODO comments.
> * Added some explanations to the cover letter (Connie, David).
> * Squashed a couple of patches together and fixed some text stuff.
>
> Looking forward to your review, or any other type of input.
>
> Halil Pasic (10):
> virtio/s390: use vring_create_virtqueue
> virtio/s390: DMA support for virtio-ccw
> virtio/s390: enable packed ring
> s390/mm: force swiotlb for protected virtualization
> s390/cio: introduce DMA pools to cio
> s390/cio: add basic protected virtualization support
> s390/airq: use DMA memory for adapter interrupts
> virtio/s390: add indirection to indicators access
> virtio/s390: use DMA memory for ccw I/O and classic notifiers
> virtio/s390: make airq summary indicators DMA
>
> arch/s390/Kconfig | 5 +
> arch/s390/include/asm/airq.h | 2 +
> arch/s390/include/asm/ccwdev.h | 4 +
> arch/s390/include/asm/cio.h | 11 ++
> arch/s390/include/asm/mem_encrypt.h | 18 +++
> arch/s390/mm/init.c | 50 +++++++
> drivers/s390/cio/airq.c | 18 ++-
> drivers/s390/cio/ccwreq.c | 8 +-
> drivers/s390/cio/cio.h | 1 +
> drivers/s390/cio/css.c | 101 +++++++++++++
> drivers/s390/cio/device.c | 65 +++++++--
> drivers/s390/cio/device_fsm.c | 40 +++---
> drivers/s390/cio/device_id.c | 18 +--
> drivers/s390/cio/device_ops.c | 21 ++-
> drivers/s390/cio/device_pgid.c | 20 +--
> drivers/s390/cio/device_status.c | 24 ++--
> drivers/s390/cio/io_sch.h | 21 ++-
> drivers/s390/virtio/virtio_ccw.c | 275 +++++++++++++++++++-----------------
> include/linux/virtio.h | 17 ---
> 19 files changed, 499 insertions(+), 220 deletions(-)
> create mode 100644 arch/s390/include/asm/mem_encrypt.h
>