On Fri, 10 Aug 2007 11:17:30 -0700
"Luck, Tony" <[email protected]> wrote:
> 1) In arch/ia64/mm/init.c: __ia64_sync_icache_dcache()
>
> - if (!pte_exec(pte))
> - return; /* not an executable page... */
> + BUG_ON(!pte_exec(pte));
>
> In this latest version the only route to this routine is from set_pte()
> inside the test :
>
> if (pte_exec(pteval) && ....) {
> }
>
> So this BUG_ON is now redundant.
>
I see.
> 2) In include/asm-ia64/pgtable.h
>
> + if (pte_exec(pteval) && // flush only new executable page.
> + pte_present(pteval) && // swap out ?
> + pte_user(pteval) && // ignore kernel page
> + (!pte_present(*ptep) ||// do_no_page or swap in, migration,
> + pte_pfn(*ptep) != pte_pfn(pteval))) // do_wp_page(), page copy
> + /* load_module() calles flush_icache_range() explicitly*/
> + __ia64_sync_icache_dcache(pteval);
>
> Just above this there is a comment saying that pte_exec() only works
> when pte_present() is true. So we must re-order the conditions so that
> we check that the pteval satisfies pte_present() before using either of
> pte_exec() or pte_user() on it like this:
>
> if (pte_present(pteval) &&
> pte_exec(pteval) &&
> pte_user(pteval) &&
>
> I put in some crude counters to see whether we should check pte_exec() or
> pte_user() next ... and it was very clear that the pte_exec() check gets
> us out of the if() faster (at least during a kernel build).
>
ok.
I'm sorry that I'll be offlined until next Wednesday. So, I'll post above
fix in a week or so.
> I also compared how often the old code called lazy_mmu_prot_update()
> with how often the new code calls __ia64_sync_icache_dcache() (again
> using kernel build as my workload) ... and the answer is about the
> same (less than 0.2% change ... probably less than run-to-run variation).
>
>
> So now the only remaining task is to convince myself that this
> new version covers all the cases.
>
yes. I want more eyes for review.
Thanks,
-Kame
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