Re: x86 ptep_get_and_clear question

[Jamie Lokier <lk@tantalophile.demon.co.uk>]

Ben LaHaise wrote:
> x86 hardware goes back to the page tables whenever there is an attempt to
> change the access it has to the pte.  Ie, if it originally accessed the
> page table for reading, it will go back to the page tables on write.  I
> believe most hardware that performs accessed/dirty bit updates in hardware
> behaves the same way.

I think the scenario in question is this:

Processor 2 has recently done some writes, so the dirty bit is set in
processor 2's TLB.

Processor 1 clears the dirty bit atomically.

Processor 2 does some more writes, and does not check the page table
because the page is already dirty in its TLB.

Result: The later writes on processor 2 do not mark the page dirty.

-- Jamie
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