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Date:   Mon, 12 Nov 2018 01:36:38 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Nadav Amit <namit@vmware.com>
Cc:     Ingo Molnar <mingo@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [PATCH v4 06/10] x86/alternative: use temporary mm for text
 poking
Message-ID: <20181112003638.GA3082@worktop>
References: <20181110231732.15060-1-namit@vmware.com>
 <20181110231732.15060-7-namit@vmware.com>
 <20181111145936.GA3021@worktop>
 <43C8C690-F079-4513-82CD-46A62DBA5A3B@vmware.com>
 <20181111235220.GB3056@worktop>
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On Mon, Nov 12, 2018 at 12:52:20AM +0100, Peter Zijlstra wrote:
> On Sun, Nov 11, 2018 at 08:53:07PM +0000, Nadav Amit wrote:
> 
> > >> +	/*
> > >> +	 * The lock is not really needed, but this allows to avoid open-coding.
> > >> +	 */
> > >> +	ptep = get_locked_pte(poking_mm, poking_addr, &ptl);
> > >> +
> > >> +	/*
> > >> +	 * If we failed to allocate a PTE, fail. This should *never* happen,
> > >> +	 * since we preallocate the PTE.
> > >> +	 */
> > >> +	if (WARN_ON_ONCE(!ptep))
> > >> +		goto out;
> > > 
> > > Since we hard rely on init getting that right; can't we simply get rid
> > > of this?

> > If it is about the way the source code looks - I guess it doesn’t sore my
> > eyes as hard as some other stuff, and I cannot do much about it (other than
> > removing it as you asked).

FWIW per the same argument we should be checking if poking_mm is !NULL.
We also don't do that.