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Subject: Re: [PATCH v7 0/7] KVM: x86: Allow Qemu/KVM to use PVH entry point
To:     Maran Wilson <maran.wilson@oracle.com>, x86@kernel.org,
        xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, jgross@suse.com
Cc:     boris.ostrovsky@oracle.com, bp@suse.de,
        dave.hansen@linux.intel.com, davem@davemloft.net,
        gregkh@linuxfoundation.org, hpa@zytor.com, jpoimboe@redhat.com,
        kirill.shutemov@linux.intel.com, linus.walleij@linaro.org,
        luto@kernel.org, mchehab@kernel.org, mingo@redhat.com,
        rdunlap@infradead.org, tglx@linutronix.de, thomas.lendacky@amd.com,
        hch@infradead.org, roger.pau@citrix.com, rkrcmar@redhat.com,
        Stefan Hajnoczi <stefanha@redhat.com>,
        Stefano Garzarella <sgarzare@redhat.com>
References: <1523920175-27287-1-git-send-email-maran.wilson@oracle.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
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Message-ID: <9aeeaf85-6ecf-c1e2-640a-657f5bb0f8ef@redhat.com>
Date:   Fri, 16 Nov 2018 11:46:28 +0100
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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:
> 
>    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.

Hi Maran, what happened to this series (and to the QEMU work)?

Paolo

> 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%)
>