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SubjectRe: [RFC PATCH v4 0/7] KVM: x86: Allow Qemu/KVM to use PVH entry point
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On 28/02/2018 19:27, Maran Wilson wrote:
> Sorry for the delay between this version and the last -- it was mostly
> due to holidays and everyone being focused on security bug mitigation
> issues. Here are the links to the previous email threads in case it is
> helpful:
>
> V3: https://lkml.org/lkml/2017/12/12/1230
> V2: https://lkml.org/lkml/2017/12/7/1624
> V1: https://lkml.org/lkml/2017/11/28/1280
>
> 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.

As you say there are many ways to achieve this and I think your choice
is fully reasonable (the other alternative that comes to mind is a "Xen
detect" function that returns a struct of function pointers).

Apart from the placement of the files, it looks great. Thanks!

Paolo

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