linux-kernel - Re: [PATCH V7 02/18] x86/fpu: Refactor arch_set_user_pkey

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Date:   Thu, 25 Nov 2021 15:23:26 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     ira.weiny@...el.com, Dave Hansen <dave.hansen@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Ira Weiny <ira.weiny@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, nvdimm@...ts.linux.dev,
        linux-mm@...ck.org
Subject: Re: [PATCH V7 02/18] x86/fpu: Refactor arch_set_user_pkey_access()

On Tue, Aug 03 2021 at 21:32, ira weiny wrote:
> +/*
> + * Replace disable bits for @pkey with values from @flags
> + *
> + * Kernel users use the same flags as user space:
> + *     PKEY_DISABLE_ACCESS
> + *     PKEY_DISABLE_WRITE
> + */
> +u32 update_pkey_val(u32 pk_reg, int pkey, unsigned int flags)

pkey_.... please.

> +{
> +	int pkey_shift = pkey * PKR_BITS_PER_PKEY;
> +
> +	/*  Mask out old bit values */
> +	pk_reg &= ~(((1 << PKR_BITS_PER_PKEY) - 1) << pkey_shift);
> +
> +	/*  Or in new values */
> +	if (flags & PKEY_DISABLE_ACCESS)
> +		pk_reg |= PKR_AD_BIT << pkey_shift;
> +	if (flags & PKEY_DISABLE_WRITE)
> +		pk_reg |= PKR_WD_BIT << pkey_shift;
> +
> +	return pk_reg;

Also this code is silly.

#define PKEY_ACCESS_MASK	(PKEY_DISABLE_ACCESS | PKEY_DISABLE_WRITE)

u32 pkey_update_pkval(u32 pkval, int pkey, u32 accessbits)
{
	int shift = pkey * PKR_BITS_PER_PKEY;

        if (WARN_ON_ONCE(accessbits & ~PKEY_ACCESS_MASK))
        	accessbits &= PKEY_ACCESS_MASK;

        pkval &= ~(PKEY_ACCESS_MASK << shift);
	return pkval | accessbit << pkey_shift;
}

See? It does not even need comments because it's self explaining and
uses sensible argument names matching the function name.