Re: [PATCH 2/2] x86: use pv-ops in {pte,pmd}_{set,clear}_flags()

[Cyrill Gorcunov <gorcunov@gmail.com>]

On Mon, Mar 31, 2014 at 09:10:07AM -0700, Linus Torvalds wrote:
> 
> It causes insane situations like this:
> 
>   #if _PAGE_BIT_FILE < _PAGE_BIT_PROTNONE
> 
> which makes no sense *except* if you think that those bits can have
> random odd hardware-defined values. But they really can't. They are
> just random bit numbers we chose.

I never understand this ifdef (I've asked once but got no reply).

> It has *also* caused horrible pain with the whole "soft dirty" thing,
> and we have absolutely ridiculous macros in pgtable-2level.h for the
> insane soft-dirty case, trying to keep the swap bits spread out "just
> right" to make soft-dirty (_PAGE_BIT_HIDDEN aka bit 11) not alias with
> the bits we use for swap offsets etc.
> 
> So how about we just say:
> 
>  - define the bits we use when PAGE_PRESENT==0 separately and explicitly
> 
>  - clean up the crazy soft-dirty crap, preferably by just making it
> depend on a 64-bit pte (so you have to have X86_PAE enabled or be on
> x86-64)

Sounds good for me, i'll try my best (if noone object).

> 
> that would sound like a good cleanup, because right now it's a
> complete nightmare to think about which bits are used how when P is 0.
> The above insane #if being the prime example of that confusion.

	Cyrill

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