Bug#561203: threads and fork on machine with VIPT-WB cache

[NIIBE Yutaka <gniibe@fsij.org>]

Thanks for your quick reply.

James Bottomley wrote:
> In COW breaking, the page table entry is copied, so A and B no longer
> have page table entries at the same physical location.  If the COW is
> intact, A and B have the same physical page, but it's also accessed by
> the same virtual address, hence no aliasing.

Let me explain more.

In the scenario, I assume:

	No aliasing between A and B.
	We have aliasing between kernel access and user access.

Before COW breaking A and B share same data (with no aliasing same
space identifier color), and B sees data in cache, while memory has
stale data.

At COW breaking, kernel copies the memory, it doesn't see new data
in cache because of aliasing.

Isn't it possible?
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