linux-kernel - Re: [RFC v6 03/62] powerpc: introduce pte_set_hash

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Message-Id: <874lu7r6qi.fsf@skywalker.in.ibm.com>
Date:   Thu, 20 Jul 2017 11:26:53 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:     Ram Pai <linuxram@...ibm.com>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org, linux-doc@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Cc:     benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
        khandual@...ux.vnet.ibm.com, bsingharora@...il.com,
        dave.hansen@...el.com, hbabu@...ibm.com, linuxram@...ibm.com,
        arnd@...db.de, akpm@...ux-foundation.org, corbet@....net,
        mingo@...hat.com, mhocko@...nel.org
Subject: Re: [RFC v6 03/62] powerpc: introduce pte_set_hash_slot() helper

Ram Pai <linuxram@...ibm.com> writes:

> Introduce pte_set_hash_slot().It  sets the (H_PAGE_F_SECOND|H_PAGE_F_GIX)
> bits at  the   appropriate   location   in   the   PTE  of  4K  PTE.  For
> 64K PTE, it  sets  the  bits  in  the  second  part  of  the  PTE. Though
> the implementation  for the former just needs the slot parameter, it does
> take some additional parameters to keep the prototype consistent.
>
> This function  will  be  handy  as  we   work   towards  re-arranging the
> bits in the later patches.
>

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
> Signed-off-by: Ram Pai <linuxram@...ibm.com>
> ---
>  arch/powerpc/include/asm/book3s/64/hash-4k.h  |   15 +++++++++++++++
>  arch/powerpc/include/asm/book3s/64/hash-64k.h |   25 +++++++++++++++++++++++++
>  2 files changed, 40 insertions(+), 0 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/book3s/64/hash-4k.h b/arch/powerpc/include/asm/book3s/64/hash-4k.h
> index d2cf949..dc153c6 100644
> --- a/arch/powerpc/include/asm/book3s/64/hash-4k.h
> +++ b/arch/powerpc/include/asm/book3s/64/hash-4k.h
> @@ -53,6 +53,21 @@ static inline int hash__hugepd_ok(hugepd_t hpd)
>  }
>  #endif
>
> +/*
> + * 4k pte format is  different  from  64k  pte  format.  Saving  the
> + * hash_slot is just a matter of returning the pte bits that need to
> + * be modified. On 64k pte, things are a  little  more  involved and
> + * hence  needs   many   more  parameters  to  accomplish  the  same.
> + * However we  want  to abstract this out from the caller by keeping
> + * the prototype consistent across the two formats.
> + */
> +static inline unsigned long pte_set_hash_slot(pte_t *ptep, real_pte_t rpte,
> +			unsigned int subpg_index, unsigned long slot)
> +{
> +	return (slot << H_PAGE_F_GIX_SHIFT) &
> +		(H_PAGE_F_SECOND | H_PAGE_F_GIX);
> +}
> +
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>
>  static inline char *get_hpte_slot_array(pmd_t *pmdp)
> diff --git a/arch/powerpc/include/asm/book3s/64/hash-64k.h b/arch/powerpc/include/asm/book3s/64/hash-64k.h
> index c281f18..89ef5a9 100644
> --- a/arch/powerpc/include/asm/book3s/64/hash-64k.h
> +++ b/arch/powerpc/include/asm/book3s/64/hash-64k.h
> @@ -67,6 +67,31 @@ static inline unsigned long __rpte_to_hidx(real_pte_t rpte, unsigned long index)
>  	return ((rpte.hidx >> (index<<2)) & 0xfUL);
>  }
>
> +/*
> + * Commit the hash slot and return pte bits that needs to be modified.
> + * The caller is expected to modify the pte bits accordingly and
> + * commit the pte to memory.
> + */
> +static inline unsigned long pte_set_hash_slot(pte_t *ptep, real_pte_t rpte,
> +		unsigned int subpg_index, unsigned long slot)
> +{
> +	unsigned long *hidxp = (unsigned long *)(ptep + PTRS_PER_PTE);
> +
> +	rpte.hidx &= ~(0xfUL << (subpg_index << 2));
> +	*hidxp = rpte.hidx  | (slot << (subpg_index << 2));
> +	/*
> +	 * Commit the hidx bits to memory before returning.
> +	 * Anyone reading  pte  must  ensure hidx bits are
> +	 * read  only  after  reading the pte by using the
> +	 * read-side  barrier  smp_rmb(). __real_pte() can
> +	 * help ensure that.
> +	 */
> +	smp_wmb();
> +
> +	/* no pte bits to be modified, return 0x0UL */
> +	return 0x0UL;
> +}
> +
>  #define __rpte_to_pte(r)	((r).pte)
>  extern bool __rpte_sub_valid(real_pte_t rpte, unsigned long index);
>  /*
> -- 
> 1.7.1