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Date: Fri, 22 Jul 2016 22:11:05 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>,
        Valdis Kletnieks <Valdis.Kletnieks@vt.edu>,
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Subject: Re: [kernel-hardening] [PATCH v5 03/32] x86/cpa: In populate_pgd,
 don't set the pgd entry until it's populated
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* Andy Lutomirski <luto@amacapital.net> wrote:

> This garbage (as evidenced by my bug and my failed attempt to fix it)
> only works if you never have a low-level page table that isn't linked
> into a higher-level page table, and it mostly requires you to do
> everything exactly the way it was originally done so all the horrible
> inline helpers don't get confused.
> 
> And AFAICT all of this was done to manually unroll a loop, and I bet
> it never sped anything up measurably even on 386 or PPro.
> 
> Whenever some vendor releases a 5 level page table CPU, can we
> *please* clean this up first?  We should have a type that points to a
> table, a different type that points to an entry (or maybe not have
> pointers to entries at all), and the levels should be referred to by
> *number*.  When you need to traverse all the way down, you write a
> *loop* instead of four bloody helper functions, some of which are
> incomprehensibly no-ops on some kernels.  And if this means that, on
> Intel, we have a silly branch in the inner loop because the bottom
> level entry format is special, who cares?
> </rant>

I'd welcome (and help out!) any effort to clean it up gradually.

Thanks,

	Ingo