Wednesday, July 10, 2019

s390x changes in QEMU 4.1

QEMU has just entered hard freeze for 4.1, so the time is here again to summarize the s390x changes for that release.

TCG

  • All instructions that have been introduced with the "Vector Facility" in the z13 machines are now emulated by QEMU. In particular, this allows Linux distributions built for z13 or later to be run under TCG (vector instructions are generated when we compile for z13; other z13 facilities are optional.)

CPU Models

  • As the needed prerequisites in TCG now have been implemented, the "qemu" cpu model now includes the "Vector Facility" and has been bumped to a stripped-down z13.
  • Models for the upcoming gen15 machines (the official name is not yet known) and some new facilities have been added.
  • If the host kernel supports it, we now indicate the AP Queue Interruption facility. This is used by vfio-ap and allows to provide interrupts for AP to the guest.

I/O Devices

  • vfio-ccw has gained support for relaying HALT SUBCHANNEL and CLEAR SUBCHANNEL requests from the guest to the device, if the host kernel vfio-ccw driver supports it. Otherwise, these instructions continue to be emulated by QEMU, as before.
  • The bios now supports IPLing (booting) from DASD attached via vfio-ccw.

Booting

  • The bios tolerates signatures written by zipl, if present; but it does not actually handle them. See the 'secure' option for zipl introduced in s390-tools 2.9.0.
And the usual fixes and cleanups.

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