linux-kernel - one question about shared mappings between user space and kernel space.

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Message-ID: <1f808b4a0909112024l11815fcbiad9a2d3748a6bafb@mail.gmail.com>
Date:	Sat, 12 Sep 2009 08:54:02 +0530
From:	Peter Chacko <peterchacko35@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: one question about shared mappings between user space and kernel 
	space.

Hi kernel geeks,

Please forgive me if this questions was asked already in the past !!!

I  have a question about shared memory mappings between kernel and
user process...(.like accessing device memory directly from user space
through device mmap interface)...I  presume this mechanism use
remap_pfn_range() or similar....when such mappings are in place, (
whats the "U/S" flag in the underlying physical page indicating CPL of
the page) for such pages ? such page  descriptors  are stored in
normal GDT  or considered as global pages ? Any special  policies of
TLB flush of  translations to such pages ?

With a shared memory between user process and kernel using such
mechanism, is it equivalent to  zero-copy transfer between user space
and kernel space? ( I mean any extra overhead in  memory access to
such pages)

I would appreciate your thoughts on this.

-- 
Best regards,
Peter Chacko

NetDiox computing systems,
Network storage & OS  training and research.
Bangalore, India.
www.netdiox.com
080 2664 0708
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