Tuesday, October 1, 2019

KVM on IBM z15 Features

To take advantage of the new features of z15, the latest addition to the IBM Z family as previously announced here, use any of the following CPU models in your guest's domain XML:
  • Pre-defined model for z15
      <cpu mode='custom'>
        <model>gen15a</model>
      </cpu>
  • Use z15 features in a migration-safe way (recommended). E.g. when running on z15 this will be a superset of the gen15a model, and feature existence will be verified on the target system prior to a live migration:
      <cpu mode='host-model'/>
  • Use z15 features in a non-migration-safe way. I.e. feature existence will not be verified on the target system prior to a live migration:
      <cpu mode='host-passthrough'/>
Here is a list of features of the new hardware generation as supported in Linux kernel 5.2 and QEMU 4.1, all activated by default in the CPU models listed above:
  • Miscellaneous Instructions
    Following the example of previous machines, new helper and general purpose instructions were
      minste3     Miscellaneous-Instruction-Extensions Facility 3 
  • SIMD Extensions
    Following up to the SIMD instructions as introduced with the previous z13 and z14 models, this feature again provides further vector instructions, which can again be used in KVM guests.
    These new vector instructions can be used to improve decimal calculations as well as for implementing high performance variants of certain cryptographic operations.
    In the z15 CPU models, the respective feature is:
      vxpdeh      Vector-Packed-Decimal-Enhancement Facility
      vxeh2       Vector enhancements facility 2
     
  • Deflate Conversion
    Provide acceleration for zlib compression and decompression
    In the z15 CPU model, the respective feature is:
      dflt        Deflate conversion facility
  • MSA Updates
    z15 introduces a new Message Security Assist MSA9, providing elliptic curve cryptography. It supports message authentication, the generation of elliptic curve keys, and scalar multiplication.
    This feature can be exploited in KVM guests' kernels and userspace applications independently (i.e. a KVM guest's userspace applications can take advantage of these features irrespective of the guest's kernel version).
    In the z15 CPU model, the respective feature is:
      msa9        Message-security-assist-extension 9 facility
      msa9_pckmo  Message-security-assist-extension 9 PCKMO
                  subfunctions for protected ECC keys
The z15 CPU model was backported into several Linux distributions. It is readily available in RHEL8.1, SLES 15 SP1 (via maintweb updates for kernel and qemu) and Ubuntu 18.04.

2 comments:

  1. Christian BornträgerNovember 13, 2019

    This is now also available in RHEL8.1 and SLES15-SP1 with latest updates (qemu and kernel)

    ReplyDelete
    Replies
    1. Adjusted in the text accordingly - thanks!

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