42fc5eae91
Let's add some documentation for the Protected VM functionality. Signed-off-by: Janosch Frank <frankja@linux.ibm.com> Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Acked-by: David Hildenbrand <david@redhat.com> Acked-by: Christian Borntraeger <borntraeger@de.ibm.com> Message-Id: <20200319131921.2367-16-frankja@linux.ibm.com> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
61 lines
2.3 KiB
ReStructuredText
61 lines
2.3 KiB
ReStructuredText
Protected Virtualization on s390x
|
|
=================================
|
|
|
|
The memory and most of the registers of Protected Virtual Machines
|
|
(PVMs) are encrypted or inaccessible to the hypervisor, effectively
|
|
prohibiting VM introspection when the VM is running. At rest, PVMs are
|
|
encrypted and can only be decrypted by the firmware, represented by an
|
|
entity called Ultravisor, of specific IBM Z machines.
|
|
|
|
|
|
Prerequisites
|
|
-------------
|
|
|
|
To run PVMs, a machine with the Protected Virtualization feature, as
|
|
indicated by the Ultravisor Call facility (stfle bit 158), is
|
|
required. The Ultravisor needs to be initialized at boot by setting
|
|
`prot_virt=1` on the host's kernel command line.
|
|
|
|
Running PVMs requires using the KVM hypervisor.
|
|
|
|
If those requirements are met, the capability `KVM_CAP_S390_PROTECTED`
|
|
will indicate that KVM can support PVMs on that LPAR.
|
|
|
|
|
|
QEMU Settings
|
|
-------------
|
|
|
|
To indicate to the VM that it can transition into protected mode, the
|
|
`Unpack facility` (stfle bit 161 represented by the feature
|
|
`unpack`/`S390_FEAT_UNPACK`) needs to be part of the cpu model of
|
|
the VM.
|
|
|
|
All I/O devices need to use the IOMMU.
|
|
Passthrough (vfio) devices are currently not supported.
|
|
|
|
Host huge page backings are not supported. However guests can use huge
|
|
pages as indicated by its facilities.
|
|
|
|
|
|
Boot Process
|
|
------------
|
|
|
|
A secure guest image can either be loaded from disk or supplied on the
|
|
QEMU command line. Booting from disk is done by the unmodified
|
|
s390-ccw BIOS. I.e., the bootmap is interpreted, multiple components
|
|
are read into memory and control is transferred to one of the
|
|
components (zipl stage3). Stage3 does some fixups and then transfers
|
|
control to some program residing in guest memory, which is normally
|
|
the OS kernel. The secure image has another component prepended
|
|
(stage3a) that uses the new diag308 subcodes 8 and 10 to trigger the
|
|
transition into secure mode.
|
|
|
|
Booting from the image supplied on the QEMU command line requires that
|
|
the file passed via -kernel has the same memory layout as would result
|
|
from the disk boot. This memory layout includes the encrypted
|
|
components (kernel, initrd, cmdline), the stage3a loader and
|
|
metadata. In case this boot method is used, the command line
|
|
options -initrd and -cmdline are ineffective. The preparation of a PVM
|
|
image is done via the `genprotimg` tool from the s390-tools
|
|
collection.
|