linux-kernel - Re: [patch V2 2/5] x86/kaiser: Simplify disabling of global pages

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Message-ID: <alpine.DEB.2.20.1711272128360.2333@nanos>
Date:   Mon, 27 Nov 2017 21:28:49 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Rik van Riel <riel@...hat.com>, daniel.gruss@...k.tugraz.at,
        hughd@...gle.com, keescook@...gle.com, linux-mm@...ck.org,
        michael.schwarz@...k.tugraz.at, moritz.lipp@...k.tugraz.at,
        richard.fellner@...dent.tugraz.at
Subject: Re: [patch V2 2/5] x86/kaiser: Simplify disabling of global pages

On Mon, 27 Nov 2017, Dave Hansen wrote:

> On 11/26/2017 03:14 PM, Thomas Gleixner wrote:
> > +static void enable_global_pages(void)
> > +{
> > +#ifndef CONFIG_KAISER
> > +	__supported_pte_mask |= _PAGE_GLOBAL;
> > +#endif
> > +}
> > +
> >  static void __init probe_page_size_mask(void)
> >  {
> >  	/*
> > @@ -179,11 +186,11 @@ static void __init probe_page_size_mask(
> >  		cr4_set_bits_and_update_boot(X86_CR4_PSE);
> >  
> >  	/* Enable PGE if available */
> > +	__supported_pte_mask |= _PAGE_GLOBAL;
> >  	if (boot_cpu_has(X86_FEATURE_PGE)) {
> >  		cr4_set_bits_and_update_boot(X86_CR4_PGE);
> > -		__supported_pte_mask |= _PAGE_GLOBAL;
> > -	} else
> > -		__supported_pte_mask &= ~_PAGE_GLOBAL;
> > +		enable_global_pages();
> > +	}
> 
> This looks a little funky.  Doesn't this or _PAGE_GLOBAL into
> __supported_pte_mask twice?  Once before the if(), and then a second
> time via enable_global_pages() inside the if?
> 
> Did you intend for it to be masked *out* in the first one and then or'd
> back in via enable_global_pages()?

It's fixed already ...