linux-kernel - Re: [RFC PATCH] x86, entry: Switch stacks on a paranoid entry from userspace

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Message-ID: <CALCETrVJE25Txr5vRKAxHpeKx9p0VJBbat44w+X4gT8qX7a4bg@mail.gmail.com>
Date:	Thu, 13 Nov 2014 15:13:38 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, Borislav Petkov <bp@...en8.de>,
	X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [RFC PATCH] x86, entry: Switch stacks on a paranoid entry from userspace

On Thu, Nov 13, 2014 at 2:47 PM, Andy Lutomirski <luto@...capital.net> wrote:
> On Thu, Nov 13, 2014 at 2:33 PM, Luck, Tony <tony.luck@...el.com> wrote:
>>> Are you sure that this works in an unmodified kernel
>>
>> Unmodified kernel has run tens of thousands of injection/consumption/recovery cycles.
>>
>> I did get a crash with the entry/exit traces you asked for.  Last 20000 lines of console log
>> attached.  There are a couple of OOPs before things fall apart completely.  I haven't yet
>> counted all the entry/exits from the last cycle to see if they match.
>>
>
> That log was a good hint, and I am a fool.  I'll send a v3 once I test it.

...or not.  I confused myself there.  I thought I had a bug, but I was wrong.

I'm stress-testing sleeping in an int3 handler that entered from user
space, and I'm not seeing any problems, even with perf firing lots of
NMIs.  I'm also passing the kprobes smoke test with my patch applied,
and the stack switching code is correctly not switching stacks.

Any chance you could try to trigger this this again with regs->sp,
regs->ip, and regs->cs added to the cpu=%d regs=... message?  I feel
like I'm missing something weird here.

--Andy

>
> I'm still unconvinced by the timeout code, though...
>
> ---Andy
>
>> -Tony
>>
>
>
>
> --
> Andy Lutomirski
> AMA Capital Management, LLC



-- 
Andy Lutomirski
AMA Capital Management, LLC
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