[Qemu-devel] [RFC v2 0/4] QEMU changes to do PVH boot

[Liam Merwick <liam.merwick@oracle.com>]

For certain applications it is desirable to rapidly boot a KVM virtual
machine. In cases where legacy hardware and software support within the
guest is not needed, QEMU should be able to boot directly into the
uncompressed Linux kernel binary with minimal firmware involvement.

There already exists an ABI to allow this for Xen PVH guests and the ABI
is supported by Linux and FreeBSD:

   https://xenbits.xen.org/docs/unstable/misc/pvh.html

Details on the Linux changes (v9 staged for 4.21): https://lkml.org/lkml/2018/12/14/1330
qboot pull request: https://github.com/bonzini/qboot/pull/17 

This patch series provides QEMU support to read the ELF header of an
uncompressed kernel binary and get the 32-bit PVH kernel entry point
from an ELF Note.  In load_linux() a call is made to load_elfboot()
so see if the header matches that of an uncompressed kernel binary (ELF)
and if so, loads the binary and determines the kernel entry address
from an ELF Note in the binary.  Then qboot does futher initialisation
of the guest (e820, etc.) and jumps to the kernel entry address and
boots the guest.

changes v1 -> v2
- Based on feedback from Stefan Hajnoczi
- The reading of the PVH entry point is now done in a single pass during
  elf_load() which results in Patch2 in v1 being split into Patches 1&2 in v2
  and considerably reworked.
- Patch1 adds a new optional function pointer to parse the ELF note type
  (the type is passed in via the existing translate_opaque arg - the
  function already had 11 args so I didn't want to add more than one new arg).
- Patch2 adds a function to elf_ops.h to find an ELF note
  matching a specific type 
- Patch3 just has a line added to the commit message to state that the Xen
  repo is the canonical location
- Patch4 (that does the PVH boot) is mainly equivalent to Patch3 in v1
  just minor load_elfboot() changes and the addition of a
  read_pvh_start_addr() helper function for load_elf()


Usіng the method/scripts documented by the NEMU team at

   https://github.com/intel/nemu/wiki/Measuring-Boot-Latency
   https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg00200.html

below are some timings measured (vmlinux and bzImage from the same build)
Time to get to kernel start is almost halved (95ṁs -> 48ms)

QEMU + qboot + vmlinux (PVH + 4.20-rc4)
 qemu_init_end: 41.550521
 fw_start: 41.667139 (+0.116618)
 fw_do_boot: 47.448495 (+5.781356)
 linux_startup_64: 47.720785 (+0.27229)
 linux_start_kernel: 48.399541 (+0.678756)
 linux_start_user: 296.952056 (+248.552515)

QEMU + qboot + bzImage:
 qemu_init_end: 29.209276
 fw_start: 29.317342 (+0.108066)
 linux_start_boot: 36.679362 (+7.36202)
 linux_startup_64: 94.531349 (+57.851987)
 linux_start_kernel: 94.900913 (+0.369564)
 linux_start_user: 401.060971 (+306.160058)

QEMU + bzImage:
 qemu_init_end: 30.424430
 linux_startup_64: 893.770334 (+863.345904)
 linux_start_kernel: 894.17049 (+0.400156)
 linux_start_user: 1208.679768 (+314.509278)


Liam Merwick (4):
  elf: Add optional function ptr to load_elf() to parse ELF notes
  elf-ops.h: Add get_elf_note_type()
  pvh: Add x86/HVM direct boot ABI header file
  pvh: Boot uncompressed kernel using direct boot ABI

 hw/alpha/dp264.c               |   4 +-
 hw/arm/armv7m.c                |   3 +-
 hw/arm/boot.c                  |   2 +-
 hw/core/generic-loader.c       |   2 +-
 hw/core/loader.c               |  24 ++++---
 hw/cris/boot.c                 |   3 +-
 hw/hppa/machine.c              |   6 +-
 hw/i386/multiboot.c            |   2 +-
 hw/i386/pc.c                   | 131 +++++++++++++++++++++++++++++++++++-
 hw/lm32/lm32_boards.c          |   6 +-
 hw/lm32/milkymist.c            |   3 +-
 hw/m68k/an5206.c               |   2 +-
 hw/m68k/mcf5208.c              |   2 +-
 hw/microblaze/boot.c           |   7 +-
 hw/mips/mips_fulong2e.c        |   5 +-
 hw/mips/mips_malta.c           |   5 +-
 hw/mips/mips_mipssim.c         |   5 +-
 hw/mips/mips_r4k.c             |   5 +-
 hw/moxie/moxiesim.c            |   2 +-
 hw/nios2/boot.c                |   7 +-
 hw/openrisc/openrisc_sim.c     |   2 +-
 hw/pci-host/prep.c             |   2 +-
 hw/ppc/e500.c                  |   3 +-
 hw/ppc/mac_newworld.c          |   5 +-
 hw/ppc/mac_oldworld.c          |   5 +-
 hw/ppc/ppc440_bamboo.c         |   2 +-
 hw/ppc/sam460ex.c              |   3 +-
 hw/ppc/spapr.c                 |   7 +-
 hw/ppc/virtex_ml507.c          |   2 +-
 hw/riscv/sifive_e.c            |   2 +-
 hw/riscv/sifive_u.c            |   2 +-
 hw/riscv/spike.c               |   2 +-
 hw/riscv/virt.c                |   2 +-
 hw/s390x/ipl.c                 |   9 ++-
 hw/sparc/leon3.c               |   3 +-
 hw/sparc/sun4m.c               |   6 +-
 hw/sparc64/sun4u.c             |   4 +-
 hw/tricore/tricore_testboard.c |   2 +-
 hw/xtensa/sim.c                |  12 ++--
 hw/xtensa/xtfpga.c             |   2 +-
 include/elf.h                  |  10 +++
 include/hw/elf_ops.h           |  72 ++++++++++++++++++++
 include/hw/loader.h            |   9 ++-
 include/hw/xen/start_info.h    | 146 +++++++++++++++++++++++++++++++++++++++++
 44 files changed, 469 insertions(+), 71 deletions(-)
 create mode 100644 include/hw/xen/start_info.h

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1.8.3.1