linux-kernel - Re: [PATCH v6] Fix INT1 Recursion with unregistered breakpoints

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Message-ID: <CAO6TR8XpdUzLX2ewpnNfL30kSJtZDSL_mi=sebceCHtEhFEjww@mail.gmail.com>
Date:	Mon, 21 Dec 2015 12:21:05 -0700
From:	Jeff Merkey <linux.mdb@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, peterz@...radead.org, luto@...nel.org
Subject: Re: [PATCH v6] Fix INT1 Recursion with unregistered breakpoints

Let me know if I need to do anything else with this patch.  I am using
git/mutt to send patches from now on and I have my smtp gateway with
gmail properly setup and tested so there won't be any more fritzed
patches.    It looks like this is relatively easy to do if you ge the
tools setup correctly.  One problem this patch did not address is
clearing the breakpoints detected as spurious in dr7.    The apps that
cause this are likely to just go back and set dr7 active again so
clearing it won't stop it from firing of again, and clearing will most
likely break most of the apps that call the breakpoint API if this
hiccup happens
intermittently.

I very much appreciate you guys patience and help it was fun to work
on this and submit these patches.  Thosmas, I must have misunderstood
the comments about magic numbers but it got corrected.

With regard to the swapgs problem, I may have a fix in the debugger to
get around it by setting the MSR if I detect someone execute one of
the swapxx instructions.  Will solve the stepping problem (tested it),
but doesn;t help with places in the exception handlers where
triggering exceptions causes swapgs to nest unexpectedly.  I will
continue to work on it and see what I can figure out that may not be
so radical as changing all the exception handlers.

Jeff
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