linux-kernel - recent x86-64 nested NMI adjustments

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Message-Id: <4F5DF5C30200007800077A5B@nat28.tlf.novell.com>
Date:	Mon, 12 Mar 2012 12:10:27 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Steven Rostedt" <rostedt@...dmis.org>
Cc:	<mingo@...e.hu>, "Peter Zijlstra" <peterz@...radead.org>,
	<linux-kernel@...r.kernel.org>, <hpa@...or.com>
Subject: recent x86-64 nested NMI adjustments

Hi Steven,

the explanation of 45d5a1683c04be28abdf5c04c27b1417e0374486
seems bogus to me: When arriving from user mode, %rsp won't point
to the user stack anymore, as it gets switched away from during the
processing of the exception (the more that the IDT entry specifies a
separate stack anyway, which even guarantees this for kernel mode
entries).

Further, a38449ef596b345e13a8f9b7d5cd9fedb8fcf921 makes the
(presumably superfluous) compare a 4-byte one, while the
documentation isn't really stating that selectors get pushed zero-
extended. Hence, if not reverting the first change altogether, I'd
minimally recommend converting the compare to a 2-byte one.

Jan

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