linux-kernel - Re: [PATCH RFC V3 2/9] x86/fpu: Refactor arch_set_user_pkey

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Date:   Tue, 13 Oct 2020 10:50:05 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     ira.weiny@...el.com, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Fenghua Yu <fenghua.yu@...el.com>, x86@...nel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvdimm@...ts.01.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH RFC V3 2/9] x86/fpu: Refactor arch_set_user_pkey_access()
 for PKS support

On 10/9/20 12:42 PM, ira.weiny@...el.com wrote:
> +/*
> + * Update the pk_reg value and return it.

How about:

	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)
> +{
> +	int pkey_shift = pkey * PKR_BITS_PER_PKEY;
> +
> +	pk_reg &= ~(((1 << PKR_BITS_PER_PKEY) - 1) << pkey_shift);
> +
> +	if (flags & PKEY_DISABLE_ACCESS)
> +		pk_reg |= PKR_AD_BIT << pkey_shift;
> +	if (flags & PKEY_DISABLE_WRITE)
> +		pk_reg |= PKR_WD_BIT << pkey_shift;

I still think this deserves two lines of comments:

	/* Mask out old bit values */

	/* Or in new values */