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

[Jürgen Groß <jgross@xxxxxxxx>]

On 22.04.25 11:20, Xin Li wrote:
> On 4/22/2025 1:59 AM, Jürgen Groß wrote:
> > 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.
> Please check https://lore.kernel.org/lkml/87y1h81ht4.ffs@tglx/.
>
> And it's was also mentioned in the previous patch:
>
> https://lore.kernel.org/lkml/20250422082216.1954310-22-xin@xxxxxxxxx/
>
> Please let me know what I have missed.
Please see my response to the previous patch.


Juergen

Attachment: OpenPGP_0xB0DE9DD628BF132F.asc
Description: OpenPGP public key

Attachment: OpenPGP_signature.asc
Description: OpenPGP digital signature