linux-kernel - Re: [PATCH v3 1/5] x86/mm: avoid redundant checking if pgprot has no change

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Date:   Tue, 4 Sep 2018 09:49:00 +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 v3 1/5] x86/mm: avoid redundant checking if pgprot has
 no change

On Tue, 4 Sep 2018, Yang, Bin wrote:
> On Mon, 2018-09-03 at 23:57 +0200, Thomas Gleixner wrote:
> > 
> > The last patch which does the overlap check is equally broken:
> 
> Sorry that I did not understand the broken of last patch.

I meant 4/5 sorry. That's the one which introduces the overlap check and
does this:

> > +       /*
> > +        * Ensure that the requested pgprot does not violate static protection
> > +        * requirements.
> > +        */
> > +       new_prot = static_protections(req_prot, address,
> > +                                     numpages << PAGE_SHIFT, pfn);
> > 
> > It expands new_prot to the whole range even if the protections only
> > overlap. That should not happen in practice, but we have no checks for that
> > at all.
> 
> Below code in patch #3 should cover this check. It will double check
> new_prot in whole large page range.

Which is exactly what is wrong. Read again what I wrote.

Thanks,

	tglx