Re: [PATCH v2 3/8] x86: Store a per-cpu shadow copy of CR4

[Thomas Gleixner]

On Fri, 24 Oct 2014, Andy Lutomirski wrote:

> Context switches and TLB flushes can change individual bits of CR4.
> CR4 reads take several cycles, so store a shadow copy of CR4 in a
> per-cpu variable.
> 
> To avoid wasting a cache line, I added the CR4 shadow to
> cpu_tlbstate, which is already touched in switch_mm.  The heaviest
> users of the cr4 shadow will be switch_mm and __switch_to_xtra, and
> __switch_to_xtra is called shortly after switch_mm during context
> switch, so the cacheline is likely to be hot.
> 
> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>

Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
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