linux-kernel - Re: [PATCH v2] MIPS64: Support of at least 48 bits of SEGBITS

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Date:	Fri, 15 May 2015 13:39:10 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>,
	aleksey.makarov@...iga.com, james.hogan@...tec.com,
	paul.burton@...tec.com, david.daney@...ium.com,
	peterz@...radead.org, linux-mips@...ux-mips.org,
	linux-kernel@...r.kernel.org, ralf@...ux-mips.org,
	davidlohr@...com, kirill@...temov.name, akpm@...ux-foundation.org,
	mingo@...nel.org
Subject: Re: [PATCH v2] MIPS64: Support of at least 48 bits of SEGBITS

Hello.

On 5/15/2015 4:34 AM, Leonid Yegoshin wrote:

> SEGBITS default is 40 bits or less, depending from CPU type.
> This patch introduces 48bits of application virtual address (SEGBITS) support.
> It is defined only for 16K and 64K pages and is optional (configurable).

> Penalty - a small number of additional pages for generic (small) applications.
> But for 64K pages it adds 3rd level of PTE structure, which has a little
> impact during software TLB refill.

> This patch is needed because MIPS I6XXX and P6XXX cores have 48 bit of
> virtual address in each segment (SEGBITS).

> Signed-off-by: Leonid Yegoshin <Leonid.Yegoshin@...tec.com>
> ---
> V2: Added correction for defintion of TASK_SIZE64
> ---
>   arch/mips/Kconfig                  |   11 +++++++++++
>   arch/mips/include/asm/pgtable-64.h |   18 +++++++++++-------
>   arch/mips/include/asm/processor.h  |    6 +++++-
>   3 files changed, 27 insertions(+), 8 deletions(-)

> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index 76efb02ae99f..3acff2f065e9 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -2032,6 +2032,17 @@ config PAGE_SIZE_64KB
>
>   endchoice
>
> +config 48VMBITS
> +	bool "48 bits virtual memory"
> +	depends on PAGE_SIZE_16KB || PAGE_SIZE_64KB
> +	depends on 64BIT
> +	help
> +	  Define a maximum at least 48 bits of application virtual memory.
> +	  Default is 40 bits or less, depending from CPU.

    s/from/on/.

> +	  In generic (small) application it is a small set of pages increase
> +	  in page tables.

    Can't parse that...

[...]
> diff --git a/arch/mips/include/asm/pgtable-64.h b/arch/mips/include/asm/pgtable-64.h
> index cf661a2fb141..c6b5473440e6 100644
> --- a/arch/mips/include/asm/pgtable-64.h
> +++ b/arch/mips/include/asm/pgtable-64.h
[...]
> @@ -114,11 +122,7 @@
>   #endif
>   #define PTRS_PER_PTE	((PAGE_SIZE << PTE_ORDER) / sizeof(pte_t))
>
> -#if PGDIR_SIZE >= TASK_SIZE64
> -#define USER_PTRS_PER_PGD	(1)
> -#else
> -#define USER_PTRS_PER_PGD	(TASK_SIZE64 / PGDIR_SIZE)
> -#endif
> +#define USER_PTRS_PER_PGD       ((TASK_SIZE64 / PGDIR_SIZE)?(TASK_SIZE64 / PGDIR_SIZE):1)

    Could write this as '(TASK_SIZE64 / PGDIR_SIZE ?: 1)'.

[...]
> diff --git a/arch/mips/include/asm/processor.h b/arch/mips/include/asm/processor.h
> index 9b3b48e21c22..bd2030f32ea4 100644
> --- a/arch/mips/include/asm/processor.h
> +++ b/arch/mips/include/asm/processor.h
> @@ -69,7 +69,11 @@ extern unsigned int vced_count, vcei_count;
>    * 8192EB ...
>    */
>   #define TASK_SIZE32	0x7fff8000UL
> -#define TASK_SIZE64	0x10000000000UL
> +#ifdef CONFIG_48VMBITS
> +#define TASK_SIZE64     (0x1UL << ((cpu_data[0].vmbits>48)?48:cpu_data[0].vmbits))

    Perhaps '(0x1UL << (min(cpu_data[0].vmbits, 48))'?

> +#else
> +#define TASK_SIZE64     (0x10000000000UL)

    Parens not needed.

[...]

WBR, Sergei

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