linux-kernel - Re: [PATCH] x86/mm: Remove in_nmi() warning from 64bit implementation of vmalloc

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Date:   Wed, 24 Apr 2019 09:31:34 +0200 (CEST)
From:   Jiri Kosina <jikos@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Joerg Roedel <jroedel@...e.de>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Nicolai Stange <nstange@...e.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/mm: Remove in_nmi() warning from 64bit implementation
 of vmalloc_fault()

On Wed, 24 Apr 2019, Peter Zijlstra wrote:

> > In-NMI warnings have been added to vmalloc_fault() via ebc8827f75 ("x86: 
> > Barf when vmalloc and kmemcheck faults happen in NMI") back in the time 
> > when our NMI entry code could not cope with nested NMIs.
> > 
> > These days, it's perfectly fine to take a fault in NMI context and we 
> > don't have to care about the fact that IRET from the fault handler might 
> > cause NMI nesting.
> > 
> > This warning has already been removed from 32bit implementation of 
> > vmalloc_fault() in 6863ea0cda8 ("x86/mm: Remove in_nmi() warning from 
> > vmalloc_fault()"), but 64bit version was omitted.
> > 
> > Remove the bogus warning also from 64bit implementation of vmalloc_fault().
> 
> Cute; did you actually trigger this?

Nope; Nicolai tripped over it while he was looking into interactions 
between ftrace and pagefaults.

> > Fixes: 6863ea0cda8 ("x86/mm: Remove in_nmi() warning from vmalloc_fault()")
> > Reported-by: Nicolai Stange <nstange@...e.de>
> > Signed-off-by: Jiri Kosina <jkosina@...e.cz>
> 
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Thanks,

-- 
Jiri Kosina
SUSE Labs