Subject: Re: [PATCH] Enable mprotect on huge pages
From: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
To: David Gibson <david@gibson.dropbear.id.au>
Cc: Andrew Morton <akpm@osdl.org>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       kenneth.w.chen@intel.com,
       "yanmin.zhang@intel.com" <yanmin.zhang@intel.com>,
       "David S. Miller" <davem@davemloft.net>,
       Paul Mackerras <paulus@samba.org>,
       Benjamin Herrenschmidt <benh@kernel.crashing.org>,
       William Lee Irwin III <wli@holomorphy.com>,
       Paul Mundt <lethal@linux-sh.org>, kkojima@rr.iij4u.or.jp,
       "Luck, Tony" <tony.luck@intel.com>
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Date: Mon, 27 Feb 2006 13:36:32 +0800
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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.


> 
> 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.


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