On Wed, 11 Mar 2020 09:21:50 -0400 Janosch Frank <fran...@linux.ibm.com> wrote:
> Lets add some documentation for the Protected VM functionality. s/Lets/Let's/ :) > > Signed-off-by: Janosch Frank <fran...@linux.ibm.com> > --- > docs/system/index.rst | 1 + > docs/system/protvirt.rst | 56 ++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 57 insertions(+) > create mode 100644 docs/system/protvirt.rst > (...) > diff --git a/docs/system/protvirt.rst b/docs/system/protvirt.rst > new file mode 100644 > index 0000000000000000..6c8cf0f7910eae86 > --- /dev/null > +++ b/docs/system/protvirt.rst > @@ -0,0 +1,56 @@ > +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. Is that specific _generations_ or specific _machines_ (i.e. those with an appropriate key)? If the latter, maybe add a note that a specific image is bound to (a) specific machine(s)? > + > + > +Prerequisites > +------------- Also, maybe add "Running PVMs requires using the KVM hypervisor." ? > + > +To run PVMs a machine with the Protected Virtualization feature > +which is indicated by the Ultravisor Call facility (stfle bit maybe s/which is/as/ ? > +158) is required. The Ultravisor needs to be initialized at boot by > +setting `prot_virt=1` on the kernel command line. > + > +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 > +`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). Stag3 does some fixups and then transfers s/Stag3/Stage3/ > +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 via 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 by genprotimg of the s390-tools package. "is done via the `genprotimg` tool from the s390-tools collection" ?
