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

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Date:	Thu, 16 Oct 2014 08:32:57 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	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 4:29 AM, Borislav Petkov <bp@...en8.de> wrote:
> 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...

That's in patch 2.  I can move it here, though.

>
> --
> Regards/Gruss,
>     Boris.
> --



-- 
Andy Lutomirski
AMA Capital Management, LLC
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