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SubjectRE: [patch] arch hook for notifying changes in PTE protections bits
>>>>> On Sat, 19 Mar 2005 12:22:20 -0800, "Seth, Rohit" <rohit.seth@intel.com> said:

Rohit> David S. Miller <mailto:davem@davemloft.net> wrote on Friday,
Rohit> March 18, 2005 8:06 PM:

>> Take a look at set_pte_at(). You get the "mm", the virtual
>> address, the pte pointer, and the new pte value.


Rohit> Thanks for pointing out the updated interface in 2.6.12-*
Rohit> kernel. I think I can overload the arch specific part of
Rohit> set_pte_at(or for that matter set_pte, as what I need is only
Rohit> pte_t) to always check if we need to do lazy I/D coherency
Rohit> for IA-64.....but this incurs extra cost for making a check
Rohit> every time set_pte_at is called. This new hook,
Rohit> lazy_mmu_prot_update, though needs to be used only when the
Rohit> permissions on a valid PTE is changing. For example, at the
Rohit> time of remap or swap, this API is not called.

Careful though: not every PTE has an associated page_map entry.

I agree about your concern about cost. Accessing the page_map is
expensive (integer division + memory access) and we have to do that in
order to find out if the page is i-cache clean.

--david
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