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

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Message-ID: <20141016081633.GG7369@worktop.fdxtended.com>
Date:	Thu, 16 Oct 2014 10:16:33 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	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 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);
> +}

I would have called these cr4_or() and cr4_nand(). When first reading
this I expected cr4_set() to be a pure write_cr4() and cr4_clear() to do
write_cr4(0) -- which obviously doesn't make too much sense.


cr4_{set,clear}_mask() might maybe be clearer but is more typing, and
the logical ops as suggested should have unambiguous meaning.
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