linux-kernel - Re: [RFC 1/5] x86: Clean up cr4 manipulation

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Message-ID: <20141016112910.GC25025@nazgul.tnic>
Date:	Thu, 16 Oct 2014 13:29:10 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...capital.net>
Cc:	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Kees Cook <keescook@...omium.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Erik Bosman <ebn310@....vu.nl>
Subject: Re: [RFC 1/5] x86: Clean up cr4 manipulation

On Thu, Oct 16, 2014 at 01:18:58PM +0200, Borislav Petkov wrote:
> On Thu, Oct 16, 2014 at 10:16:33AM +0200, Peter Zijlstra wrote:
> > On Tue, Oct 14, 2014 at 03:57:35PM -0700, Andy Lutomirski wrote:
> > > +/* Set in this cpu's CR4. */
> > > +static inline void cr4_set(unsigned long mask)
> > > +{
> > > +	unsigned long cr4;
> > > +
> > > +	cr4 = read_cr4();
> > > +	cr4 |= mask;
> > > +	write_cr4(cr4);
> > > +}
> > > +
> > > +/* Clear in this cpu's CR4. */
> > > +static inline void cr4_clear(unsigned long mask)
> > > +{
> > > +	unsigned long cr4;
> > > +
> > > +	cr4 = read_cr4();
> > > +	cr4 &= ~mask;
> > > +	write_cr4(cr4);
> > > +}

Btw, on a related note, we probably should check whether the bits we
want to set/clear are already set/cleared and then save us the CR4
write.

It probably won't be the case all that much but still...

-- 
Regards/Gruss,
    Boris.
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