linux-kernel - Re: [PATCH 2/7] openrisc: fix PTRS_PER

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Message-ID: <57DFF5BA.6090400@southpole.se>
Date:   Mon, 19 Sep 2016 16:27:06 +0200
From:   Jonas Bonn <jonas@...thpole.se>
To:     Stafford Horne <shorne@...il.com>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/7] openrisc: fix PTRS_PER_PGD define

On 09/16/2016 04:43 PM, Stafford Horne wrote:
> From: Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>
>
> On OpenRISC, with its 8k pages, PAGE_SHIFT is defined to be 13.
> That makes the expression (1UL << (PAGE_SHIFT-2)) evaluate
> to 2048.
> The correct value for PTRS_PER_PGD should be 256.
>
> Correcting the PTRS_PER_PGD define unveiled a bug in map_ram(),
> where PTRS_PER_PGD was used when the intent was to iterate
> over a set of page table entries.
> This patch corrects that issue as well.
>
> Signed-off-by: Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>
> Signed-off-by: Stafford Horne <shorne@...il.com>
Acked-by: Jonas Bonn <jonas@...thpole.se>

> ---
>   arch/openrisc/include/asm/pgtable.h | 2 +-
>   arch/openrisc/mm/init.c             | 2 +-
>   2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/openrisc/include/asm/pgtable.h b/arch/openrisc/include/asm/pgtable.h
> index 69c7df0..3567aa7 100644
> --- a/arch/openrisc/include/asm/pgtable.h
> +++ b/arch/openrisc/include/asm/pgtable.h
> @@ -69,7 +69,7 @@ extern void paging_init(void);
>    */
>   #define PTRS_PER_PTE	(1UL << (PAGE_SHIFT-2))
>   
> -#define PTRS_PER_PGD	(1UL << (PAGE_SHIFT-2))
> +#define PTRS_PER_PGD	(1UL << (32-PGDIR_SHIFT))
>   
>   /* calculate how many PGD entries a user-level program can use
>    * the first mappable virtual address is 0
> diff --git a/arch/openrisc/mm/init.c b/arch/openrisc/mm/init.c
> index 7f94652..b782ce9 100644
> --- a/arch/openrisc/mm/init.c
> +++ b/arch/openrisc/mm/init.c
> @@ -110,7 +110,7 @@ static void __init map_ram(void)
>   			set_pmd(pme, __pmd(_KERNPG_TABLE + __pa(pte)));
>   
>   			/* Fill the newly allocated page with PTE'S */
> -			for (j = 0; p < e && j < PTRS_PER_PGD;
> +			for (j = 0; p < e && j < PTRS_PER_PTE;
>   			     v += PAGE_SIZE, p += PAGE_SIZE, j++, pte++) {
>   				if (v >= (u32) _e_kernel_ro ||
>   				    v < (u32) _s_kernel_ro)