Re: [RFC PATCH v2 22/34] x86/msr: Utilize the alternatives mechanism to read MSR

[Jürgen Groß <jgross@xxxxxxxx>]

On 22.04.25 10:22, Xin Li (Intel) wrote:
> To eliminate the indirect call overhead introduced by the pv_ops API,
> utilize the alternatives mechanism to read MSR:
>
>      1) When built with !CONFIG_XEN_PV, X86_FEATURE_XENPV becomes a
>         disabled feature, preventing the Xen code from being built
>         and ensuring the native code is executed unconditionally.
>
>      2) When built with CONFIG_XEN_PV:
>
>         2.1) If not running on the Xen hypervisor (!X86_FEATURE_XENPV),
>              the kernel runtime binary is patched to unconditionally
>              jump to the native MSR read code.
>
>         2.2) If running on the Xen hypervisor (X86_FEATURE_XENPV), the
>              kernel runtime binary is patched to unconditionally jump
>              to the Xen MSR read code.
>
> The alternatives mechanism is also used to choose the new immediate
> form MSR read instruction when it's available.
>
> Consequently, remove the pv_ops MSR read APIs and the Xen callbacks.
Same as the comment to patch 5: there is no indirect call overhead after
the system has come up.


Juergen

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