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

[Maran Wilson]

Friendly ping. I am hopeful one of the x86 and/or KVM maintainers has a 
few cycles to spare to look this over.

And thanks to everyone who has helped thus far by providing valuable 
feedback and reviewing.

ÂÂ https://lkml.org/lkml/2018/4/16/1002

Thanks,
-Maran

On 4/16/2018 4:09 PM, 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:
>
>     https://xenbits.xen.org/docs/unstable/misc/pvh.html
>
> This patch series would enable Qemu to use that same entry point for
> booting KVM guests.
>
> 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
>     arch/x86/platform/pvh/{enlighten.c,head.S}
>   * 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
>     cases.
>
>
> Maran Wilson (7):
>    xen/pvh: Split CONFIG_XEN_PVH into CONFIG_PVH and CONFIG_XEN_PVH
>    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
>      file
>    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%)