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Date: Fri, 7 Apr 2017 16:45:26 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Mathias Krause <minipli@googlemail.com>
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Subject: Re: [kernel-hardening] Re: [RFC v2][PATCH 04/11] x86: Implement
 __arch_rare_write_begin/unmap()
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On Fri, Apr 07, 2017 at 12:51:15PM +0200, Mathias Krause wrote:
> Why that? It allows fast and CPU local modifications of r/o memory.
> OTOH, an approach that needs to fiddle with page table entries
> requires global synchronization to keep the individual TLB states in
> sync. Hmm.. Not that fast, I'd say.

The fixmaps used for kmap_atomic are per-cpu, no global sync required.