linux-kernel - Re: [PATCH v12 05/22] selftests/vm: generic function to handle shadow key register

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Date:   Fri, 16 Mar 2018 15:05:19 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Ram Pai <linuxram@...ibm.com>, shuahkh@....samsung.com,
        linux-kselftest@...r.kernel.org
Cc:     mpe@...erman.id.au, linuxppc-dev@...ts.ozlabs.org,
        linux-mm@...ck.org, x86@...nel.org, linux-arch@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        mingo@...hat.com, akpm@...ux-foundation.org,
        benh@...nel.crashing.org, paulus@...ba.org,
        khandual@...ux.vnet.ibm.com, aneesh.kumar@...ux.vnet.ibm.com,
        bsingharora@...il.com, hbabu@...ibm.com, mhocko@...nel.org,
        bauerman@...ux.vnet.ibm.com, ebiederm@...ssion.com, arnd@...db.de
Subject: Re: [PATCH v12 05/22] selftests/vm: generic function to handle shadow
 key register

On 02/21/2018 05:55 PM, Ram Pai wrote:
> +static inline u32 pkey_to_shift(int pkey)
> +{
> +	return pkey * PKEY_BITS_PER_PKEY;
> +}

pkey_bit_position(), perhaps?

> +static inline pkey_reg_t reset_bits(int pkey, pkey_reg_t bits)
> +{
> +	u32 shift = pkey_to_shift(pkey);
> +
> +	return ~(bits << shift);
> +}

I'd prefer clear_pkey_flags() or maybe clear_pkey_bits().  "reset" can
mean "reset to 0" or "reset to 1".

Also, why the u32 here?  Isn't an int more appropriate?

> +static inline pkey_reg_t left_shift_bits(int pkey, pkey_reg_t bits)
> +{
> +	u32 shift = pkey_to_shift(pkey);
> +
> +	return (bits << shift);
> +}
> +
> +static inline pkey_reg_t right_shift_bits(int pkey, pkey_reg_t bits)
> +{
> +	u32 shift = pkey_to_shift(pkey);
> +
> +	return (bits >> shift);
> +}

Some comments on these would be handy.  Basically that this takes a
per-key flags value and puts it at the right position so it can be
shoved in the register.