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Date:   Wed, 30 Oct 2019 11:04:18 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
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Subject: Re: [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user
 mappings
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On Tue, Oct 29, 2019 at 05:27:43PM +0000, Edgecombe, Rick P wrote:
> On Mon, 2019-10-28 at 22:00 +0100, Peter Zijlstra wrote:

> > That should be limited to the module range. Random data maps could
> > shatter the world.
> 
> BPF has one vmalloc space allocation for the byte code and one for the module
> space allocation for the JIT. Both get RO also set on the direct map alias of
> the pages, and reset RW when freed.

Argh, I didn't know they mapped the bytecode RO; why does it do that? It
can throw out the bytecode once it's JIT'ed.

> You mean shatter performance?

Shatter (all) large pages.