Re: [RFC 2/5] x86: Store a per-cpu shadow copy of CR4

[Peter Zijlstra]

On Tue, Oct 14, 2014 at 03:57:36PM -0700, 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 during context switches.

I'm a little confused. We should be more specific I suppose, context
switches don't always change mm, but CR4 state is per task.

>From a quick look, only switch_mm() pokes at tlb, switch_to() does not.


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