Re: [PATCH-4.16 v2] x86/xstate: reset cached register values on resume

[Ian Jackson <iwj@xxxxxxxxxxxxxx>]

Marek Marczykowski-Górecki writes ("[PATCH-4.16 v2] x86/xstate: reset cached 
register values on resume"):
> set_xcr0() and set_msr_xss() use cached value to avoid setting the
> register to the same value over and over. But suspend/resume implicitly
> reset the registers and since percpu areas are not deallocated on
> suspend anymore, the cache gets stale.
> Reset the cache on resume, to ensure the next write will really hit the
> hardware. Choose value 0, as it will never be a legitimate write to
> those registers - and so, will force write (and cache update).
> 
> Note the cache is used io get_xcr0() and get_msr_xss() too, but:
> - set_xcr0() is called few lines below in xstate_init(), so it will
>   update the cache with appropriate value
> - get_msr_xss() is not used anywhere - and thus not before any
>   set_msr_xss() that will fill the cache
> 
> Fixes: aca2a985a55a "xen: don't free percpu areas during suspend"
> Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> Changes in v2:
>  - adjust xss init value per Jan request
> 
> For 4.16: this unbreaks S3 resume, it was posted initially back in
> August and is shipped in Qubes since September (although backported to
> 4.14, not unstable) with no reported regressions.

Thank you.  I went back and read the thread.  Thanks to everyone who
contributed there.

Release-Acked-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>