RE: [patch] arch hook for notifying changes in PTE protections bits

[David Mosberger <davidm@napali.hpl.hp.com>]

>>>>> 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