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

[Jürgen Groß]

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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