linux-kernel - Re: Perf: WARNING: arch/x86/entry/common.c:624 idtentry_exit_cond

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Message-ID: <87d064d13p.fsf@nanos.tec.linutronix.de>
Date:   Fri, 12 Jun 2020 12:34:18 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        open list <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>, cj.chengjian@...wei.com,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michel Lespinasse <walken@...gle.com>,
        lkft-triage@...ts.linaro.org,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: Perf: WARNING: arch/x86/entry/common.c:624 idtentry_exit_cond_rcu+0x92/0xc0

Andy Lutomirski <luto@...capital.net> writes:
>> On Jun 12, 2020, at 2:01 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
>> There is no IST on 32bit, never was. We do software stack switching for
>> device interrupts, but that's a different story.
>> 
>
> DEFINE_IDTENTRY does the idtentry_enter_cond_rcu() dance, which isn’t
> intended to be safe from NMI context.  It should probably map to
> DEFINE_IDTENTRY_RAW() instead.  The specific issue is that NMI ends up
> there, and at least DEFINE_IDTENTRY_NMI should be raw.

Yes, you are right. That's clearly broken. 

> I haven’t tried this at all, nor have I dug through all the users of
> these macros to check what they expect.  Perhaps we should not have
> the _IST one defined at all on 32 bit and rename it to
> DEFINE_IDTENTRY_IST_RAW on 64 bit to make it more clear what’s going
> on when reading the C code.

Let me go over it with a fine comb.

> Or maybe I’m too sleepy and I’m nuts. But I don’t think I am.

/me politely refrains from commenting