linux-kernel - Re: [PATCH] x86/mm: fix cpu stuck issue in __change_page_attr_set

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Date:   Mon, 16 Jul 2018 09:48:28 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Yang, Bin" <bin.yang@...el.com>
cc:     "mingo@...nel.org" <mingo@...nel.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Gross, Mark" <mark.gross@...el.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>
Subject: Re: [PATCH] x86/mm: fix cpu stuck issue in
 __change_page_attr_set_clr

On Tue, 10 Jul 2018, Yang, Bin wrote:
> > +	 * FIXME:
> > +	 * 1) Make this yell loudly if something tries to set a full
> > +	 *    large page to something which is not allowed.
> 
> I am trying to work out a patch based on your sample code and
> comments. 
> I do not understand here why it needs to yell loudly if set a full
> large page to something which is not allowed. It can split the large
> page to 4K-pages finally. And static_protection() will also be called
> for 4K-page change. Why not just add warning if 4K-page change is not
> allowed?

Think about it. If there is a large page which contains an area which
requires a different mapping that the one which the large page provides,
then something went wrong _before_ this code is called.

Thanks,

	tglx