Re: [PATCH] x86/MTRR: constrain AP sync and BSP restore

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Mar 27, 2025 at 10:54:23AM +0100, Jan Beulich wrote:
> mtrr_set_all() has quite a bit of overhead, which is entirely useless
> when set_mtrr_state() really does nothing. Furthermore, with
> mtrr_state.def_type never initialized from hardware, post_set()'s
> unconditional writing of the MSR means would leave us running in UC
> mode after the sync.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> --- a/xen/arch/x86/cpu/mtrr/main.c
> +++ b/xen/arch/x86/cpu/mtrr/main.c
> @@ -605,13 +605,15 @@ void mtrr_aps_sync_begin(void)
>  
>  void mtrr_aps_sync_end(void)
>  {
> -     set_mtrr(~0U, 0, 0, 0);
> +     if (mtrr_if)
> +             set_mtrr(~0U, 0, 0, 0);
>       hold_mtrr_updates_on_aps = 0;
>  }
>  
>  void mtrr_bp_restore(void)

Maybe I'm blind, but I cannot find any caller to mtrr_bp_restore()?
Am I missing something obvious?

Thanks, Roger.