Blaisorblade wrote:
On Tuesday 02 May 2006 05:53, Nick Piggin wrote:
[email protected] wrote:
From: Paolo 'Blaisorblade' Giarrusso <[email protected]>
pte_present(pte) implies that pte_pfn(pte) is valid. Normally even with a
_PAGE_PROTNONE pte this holds, but not when such a PTE is installed by
the new install_file_pte; previously it didn't store protections, only
file offsets, with the patches it also stores protections, and can set
_PAGE_PROTNONE|_PAGE_FILE.
What could be done is to set a PTE with "no protection", use another bit
rather than _PAGE_PROTNONE. This wastes one more bit but doable.
I see.
Why is this combination useful? Can't you just drop the _PAGE_FILE from
_PAGE_PROTNONE ptes?
I must think on this, but the semantics are not entirely the same between the
two cases.
And yes, this won't work. I was misunderstanding what was happening.
I guess your problem is that you're overloading the pte protection bits
for present ptes as protection bits for not present (file) ptes. I'd rather
you just used a different encoding for file pte protections then.
"Wasting" a bit seems much more preferable for this very uncommon case (for
most people) rather than bloating pte_present check, which is called in
practically every performance critical inner loop).
That said, if the patch is i386/uml specific then I don't have much say in
it. If Ingo/Linus and Jeff/Yourself, respectively, accept the patch, then
fine.
But I think you should drop the comment from the core code. It seems wrong.
--
SUSE Labs, Novell Inc.
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