linux-kernel - Re: [PATCH RESEND] powerpc: fix usage of _PAGE

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Date:   Mon, 19 Sep 2016 11:30:12 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Scott Wood <oss@...error.net>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH RESEND] powerpc: fix usage of _PAGE_RO in hugepage

Christophe Leroy <christophe.leroy@....fr> writes:

> On some CPUs like the 8xx, _PAGE_RW hence _PAGE_WRITE is defined
> as 0 and _PAGE_RO has to be set when a page is not writable
>
> _PAGE_RO is defined by default in pte-common.h, however BOOK3S/64
> doesn't include that file so _PAGE_RO has to be defined explicitly
> in book3s/64/pgtable.h
>
> fixes: a7b9f671f2d14 ("powerpc32: adds handling of _PAGE_RO")
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> ---
> This patch was initially part of the v1 serie of patchs for providing
> hugepage support to the 8xx. As suggested by Aneesh, that serie has
> been splited to focus only on hugepage implementation for 8xx.
> This patch is a fix and is independant of 8xx hugepage implementation,
> allthough it is required to have hugepage support working properly on
> the 8xx.
>
>  arch/powerpc/include/asm/book3s/64/pgtable.h | 2 ++
>  arch/powerpc/mm/hugetlbpage.c                | 2 ++
>  2 files changed, 4 insertions(+)
>
> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
> index 8ec8be9..9fd77f8 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> @@ -6,6 +6,8 @@
>   */
>  #define _PAGE_BIT_SWAP_TYPE	0
>  
> +#define _PAGE_RO		0
> +
>  #define _PAGE_EXEC		0x00001 /* execute permission */
>  #define _PAGE_WRITE		0x00002 /* write access allowed */
>  #define _PAGE_READ		0x00004	/* read access allowed */
> diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
> index 7372ee1..8a512b1 100644
> --- a/arch/powerpc/mm/hugetlbpage.c
> +++ b/arch/powerpc/mm/hugetlbpage.c
> @@ -1021,6 +1021,8 @@ int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
>  	mask = _PAGE_PRESENT | _PAGE_READ;
>  	if (write)
>  		mask |= _PAGE_WRITE;
> +	else
> +		mask |= _PAGE_RO;
>  
>  	if ((pte_val(pte) & mask) != mask)
>  		return 0;
> -- 

Can you add the commit message also as code comment ?. It is confusing
to find that we do mask = _PAGE_READ and then mask |= _PAGE_RO.

Otherwise

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>

-aneesh