Re: Remapping pages mapped to userspace (was: [PATCH 10 of 20]ipath - support for userspace apps using core driver)

[Bryan O'Sullivan]

On Fri, 2006-03-17 at 17:13 +0000, Hugh Dickins wrote:

> You seem to be asking to "revoke" an mmap:

Yes.  We'd like this ability, too.

> Though it looks like subsequent userspace accesses will then go to
> do_anonymous_page, giving ZERO_PAGE to read faults or a fresh anon
> page to write faults: I think I'd prefer it if pte_none accesses in
> a VM_PFNMAP area gave SIGBUS, but unsure if we can change that now.

It would be unfortunate if userspace were spinning on a chip register,
waiting for the register to transition from zero to non-zero, and we
replaced that mapping with an anonymous page.  In that case, userspace
could potentially spin forever, having no way to detect the demise of
the device.

	<b

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