Re: [PATCH] Enable mprotect on huge pages

[David Gibson <david@gibson.dropbear.id.au>]

On Mon, Feb 27, 2006 at 01:36:32PM +0800, Zhang, Yanmin wrote:
> On Mon, 2006-02-27 at 07:09, David Gibson wrote:
> > On Fri, Feb 24, 2006 at 02:28:44PM -0800, Andrew Morton wrote:
> > > "Zhang, Yanmin" <yanmin_zhang@linux.intel.com> wrote:
> > > >
> > > > From: Zhang, Yanmin <yanmin.zhang@intel.com>
> > > > 
> > > > 2.6.16-rc3 uses hugetlb on-demand paging, but it doesn_t support hugetlb
> > > > mprotect. My patch against 2.6.16-rc3 enables this capability.
> > > > 
> > > 
> > > Well I suppose that makes sense.  It does assume that the normal pte
> > > protection-changing APIs do the right thing on all architectures which
> > > implement huge pages.  That's quite possibly the case, but we should
> > > confirm that.
> > 
> > Well, it will need to be huge_ptep_get_and_clear() below, not the
> > normal version.
> I will change it.
> 
> 
> >   But pte_modify should be ok.  I'm not sure
> > pte_present() is safe, either, !pte_none() is what we use elsewhere in
> > hugetlb.c.
> pte_present is used in some files while !pte_none is used 
> in other files. Anyway, I will change it to !pte_none.

But most importantly, pte_present() is not used in mm/hugetlb.c, the
generic part of the code.

> > And.. looks like lazy_mmu_prot_update() is unsafe, too.  The only arch
> > which has something here (ia64) has a function which does icache
> > flushes on PAGE_SIZE only.
> I already sent another patch to ia64 maillist to fix the issue.
> See http://marc.theaimsgroup.com/?l=linux-ia64&m=114066414720468&w=2
> 
> Thanks.
> 
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson
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