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Re: [Xen-devel] [PATCH v7 0/7] KVM: x86: Allow Qemu/KVM to use PVH entry point

On 11/16/2018 2:46 AM, Paolo Bonzini wrote:
On 17/04/18 01:09, Maran Wilson wrote:
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 without the need to run firmware.

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


This patch series would enable Qemu to use that same entry point for
booting KVM guests.
Hi Maran, what happened to this series (and to the QEMU work)?

Hi Paolo,

Thank you for the reminder. Sorry, I have been wanting to continue this work for a while now, but our team has been pulled in other directions and this one ended up getting temporarily pushed down the priority stack.

Let me discuss with my management and get back to you. I do want (and intend) to support and push this over the finish line.

In the meantime, if there are any folks out there with a specific business need for getting this done sooner rather than later and are able to invest a bit of time to collaborate on the remaining Qemu work, please feel free to ping me offline. We have some preliminary Qemu patches, but there is some additional work needed before they are ready wider review.



Changes from v6:

  * Addressed issues caught by the kbuild test robot:
     - Restored an #include line that had been dropped by mistake (patch 4)
     - Removed a pair of #include lines that were no longer needed in a
       common code file and causing problems for certain 32-bit configs
       (patchs 4 and 7)

Changes from v5:

  * The interface changes to the x86/HVM start info layout have
    now been accepted into the Xen tree.
  * Rebase and merge upstream PVH file changes.
  * (Patch 6) Synced up to the final version of the header file that was
              acked and pulled into the Xen tree.
  * (Patch 1) Fixed typo and removed redundant "def_bool n" line.

Changes from v4:

Note: I've withheld Juergen's earlier "Reviewed-by" tags from patches
1 and 7 since there were minor changes (mostly just addition of
CONFIG_KVM_GUEST_PVH as requested) that came afterwards.

  * Changed subject prefix from RFC to PATCH
  * Added CONFIG_KVM_GUEST_PVH as suggested
  * Relocated the PVH common files to
  * Realized I also needed to move the objtool override for those files
  * Updated a few code comments per reviewer feedback
  * Sent out a patch of the hvm_start_info struct changes against the Xen
    tree since that is the canonical copy of the header. Discussions on
    that thread have resulted in some (non-functional) updates to
    start_info.h (patch 6/7) and those changes are reflected here as well
    in order to keep the files in sync. The header file has since been
    ack'ed for the Xen tree by Jan Beulich.

Changes from v3:

  * Implemented Juergen's suggestion for refactoring and moving the PVH
    code so that CONFIG_XEN is no longer required for booting KVM guests
    via the PVH entry point.
    Functionally, nothing has changed from V3 really, but the patches
    look completely different now because of all the code movement and
    refactoring. Some of these patches can be combined, but I've left
    them very small in some cases to make the refactoring and code
    movement easier to review.
    My approach for refactoring has been to create a PVH entry layer that
    still has understanding and knowledge about Xen vs non-Xen guest types
    so that it can make run time decisions to handle either case, as
    opposed to going all the way and re-writing it to be a completely
    hypervisor agnostic and architecturally pure layer that is separate
    from guest type details. The latter seemed a bit overkill in this
    situation. And I've handled the complexity of having to support
    Qemu/KVM boot of kernels compiled with or without CONFIG_XEN via a
    pair of xen specific __weak routines that can be overridden in kernels
    that support Xen guests. Importantly, the __weak routines are for
    xen specific code only (not generic "guest type" specific code) so
    there is no clashing between xen version of the strong routine and,
    say, a KVM version of the same routine. But I'm sure there are many
    ways to skin this cat, so I'm open to alternate suggestions if there
    is a compelling reason for not using __weak in this situation.

Changes from v2:

  * All structures (including memory map table entries) are padded and
    aligned to an 8 byte boundary.

  * Removed the "packed" attributes and made changes to comments as
    suggested by Jan.

Changes from v1:

  * Adopted Paolo's suggestion for defining a v2 PVH ABI that includes the
    e820 map instead of using the second module entry to pass the table.

  * Cleaned things up a bit to reduce the number of xen vs non-xen special

Maran Wilson (7):
   xen/pvh: Move PVH entry code out of Xen specific tree
   xen/pvh: Create a new file for Xen specific PVH code
   xen/pvh: Move Xen specific PVH VM initialization out of common file
   xen/pvh: Move Xen code for getting mem map via hcall out of common
   xen/pvh: Add memory map pointer to hvm_start_info struct
   KVM: x86: Allow Qemu/KVM to use PVH entry point

  MAINTAINERS                                     |   1 +
  arch/x86/Kbuild                                 |   2 +
  arch/x86/Kconfig                                |  14 +++
  arch/x86/kernel/head_64.S                       |   2 +-
  arch/x86/platform/pvh/Makefile                  |   5 +
  arch/x86/platform/pvh/enlighten.c               | 136 ++++++++++++++++++++++++
  arch/x86/{xen/xen-pvh.S => platform/pvh/head.S} |   0
  arch/x86/xen/Kconfig                            |   3 +-
  arch/x86/xen/Makefile                           |   2 -
  arch/x86/xen/enlighten_pvh.c                    |  93 +++-------------
  include/xen/interface/hvm/start_info.h          |  63 ++++++++++-
  11 files changed, 240 insertions(+), 81 deletions(-)
  create mode 100644 arch/x86/platform/pvh/Makefile
  create mode 100644 arch/x86/platform/pvh/enlighten.c
  rename arch/x86/{xen/xen-pvh.S => platform/pvh/head.S} (100%)

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