linux-kernel - Re: [PATCH] Fix int1 recursion with unregistered breakpoints

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Message-ID: <CAO6TR8XnVrkSuA6gGq5o6Y=o+kV=3aZZKzNyo+wjYVviYA8ODw@mail.gmail.com>
Date:	Mon, 14 Dec 2015 14:40:59 -0700
From:	Jeff Merkey <linux.mdb@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	mingo@...hat.com, x86@...nel.org, peterz@...radead.org,
	luto@...nel.org
Subject: Re: [PATCH] Fix int1 recursion with unregistered breakpoints

On 12/14/15, H. Peter Anvin <hpa@...or.com> wrote:
> On 12/14/15 13:03, Jeff Merkey wrote:
>> Please consider the attached patch.
>>
>> I have reviewed all the code that touches this patch and have
>> determined it will function and support all of the software that
>> depends on this handler properly.  I have compiled and tested this
>> patch with a test harness that tests the robustness of the linux
>> breakpoint API and handlers in the following ways:
>>
>> 1.  Setting multiple conditional breakpoints through
>> arch_install_hw_breakpoint API across four processors to test the rate
>> at which the interface can handle breakpoint exceptions
>>
>> 2.  Setting unregistered breakpoints to test the handlers robustness
>> in dealing with error handling conditions and errant or spurious
>> hardware conditions and to simulate actual "lazy debug register
>> switching" (which does not work BTW) with null bp handlers to test the
>> robustness of the handlers.
>>
>> 3.  Clearing and setting breakpoints across multiple processors then
>> triggering concurrent exceptions in both interrupt and process
>> contexts.
>>
>> This patch improves robustness in several ways in the linux kernel:
>>
>> 1.  Corrects bug in handling unregistered breakpoints.
>>
>> 2.  Provides hardware check of dr7 to determine source of breakpoint
>> if OS cannot ascertain the int1 source from its own state and
>> variables.
>>
>> 3.  Actually allows "lazy debug register switching" to function, which
>> until recently has apparently never been actually seen on live
>> hardware or actually tested.
>>
>
> This is all fine and good, but you are missing one of the most important
> parts of a patch: a patch description, describing in detail the problem
> that it solves and why.  This description needs to be comprehensible not
> just for people already initiated but for someone doing code archaeology
> a decade from now.
>
> Thanks,
>
> 	-hpa
>
>
>

Yes sir, I'll get that added right away.

Jeff
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