Re: [PATCH] ppc64: Fix possible race with set_pte on a present PTE

[Linus Torvalds]

On Wed, 26 May 2004, Andrea Arcangeli wrote:
> 
> after various searching on the x86 docs I found:
> 
> 	Whenever a page-directory or page-table entry is changed (including when
> 	the present flag is set to zero), the operating-system must immediately
> 	invalidate the corresponding entry in the TLB so that it can be updated
> 	the next time the entry is referenced.
> 
> according to the above we'd need to flush the tlb even in
> do_anonymous_page on x86, or am I reading it wrong?

You're reading it wrong.

The "including when the present flag is set to zero" part does not mean 
that the present flag was zero _before_, it means "is being set to zero" 
as in "having been non-zero before that".

Anytime the P flag was clear _before_, we don't need to invalidate, 
because non-present entries are not cached in the TLB.

			Linus
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