Re: [Xen-devel] [PATCH 2/2] x86: add pte_set_flags/clear_flags for pteflag manipulation

[Jeremy Fitzhardinge <jeremy@goop.org>]

Jan Beulich wrote:
> I think a comment (or event a BUG_ON()) should be added here to make
> clear that this absolutely must not be used to toggle the present bit. I
> even view toggling _PAGE_PSE as dangerous this way.
>
> And alternative would be to make these macros and #undef them (or keep
> them inline functions but add destructive #define-s) after all their users.
>   

I don't see any particular problem with changing PSE or even Present 
with these functions; they don't operate on live in-memory ptes, so its 
not like they could ever be used to modify a pte unless followed with 
some kind of set_pte operation.  It is unwise to change any pte flag 
without knowing what you're doing (though P or PSE would probably have 
less subtle effects than some of the others).

But it probably wouldn't hurt to have a __ prefix to indicate they're 
"internal" and not for general use.

    J