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

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Date:	Fri, 15 May 2015 13:49:35 -0700
From:	David Daney <ddaney.cavm@...il.com>
To:	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>
CC:	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

On 05/14/2015 06:34 PM, 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).
>

Those processors don't require the patch.  You wrote the patch to give a 
larger VA space at the request of kernel users.  So perhaps say:

   The patch (optionally) increases the VA space available to userspace 
processes from N-bits to 48-bits


> 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

Should probabaly be called VABITS instead of VMBITS to match the terms 
used in the architecture reference manuals, as well as other ports (ARM64).

Perhaps MIPS_VA_BITS_48


> +	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.
> +	  In generic (small) application it is a small set of pages increase
> +	  in page tables.
> +	  If unsure, say N.
> +
>   config FORCE_MAX_ZONEORDER
>   	int "Maximum zone order"
>   	range 14 64 if MIPS_HUGE_TLB_SUPPORT && PAGE_SIZE_64KB
> 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
> @@ -17,7 +17,7 @@
>   #include <asm/cachectl.h>
>   #include <asm/fixmap.h>
>
> -#ifdef CONFIG_PAGE_SIZE_64KB
> +#if defined(CONFIG_PAGE_SIZE_64KB) && !defined(CONFIG_48VMBITS)
>   #include <asm-generic/pgtable-nopmd.h>
>   #else
>   #include <asm-generic/pgtable-nopud.h>
> @@ -90,7 +90,11 @@
>   #define PTE_ORDER		0
>   #endif
>   #ifdef CONFIG_PAGE_SIZE_16KB
> -#define PGD_ORDER		0
> +#ifdef CONFIG_48VMBITS
> +#define PGD_ORDER               1
> +#else
> +#define PGD_ORDER               0
> +#endif
>   #define PUD_ORDER		aieeee_attempt_to_allocate_pud
>   #define PMD_ORDER		0
>   #define PTE_ORDER		0
> @@ -104,7 +108,11 @@
>   #ifdef CONFIG_PAGE_SIZE_64KB
>   #define PGD_ORDER		0
>   #define PUD_ORDER		aieeee_attempt_to_allocate_pud
> +#ifdef CONFIG_48VMBITS
> +#define PMD_ORDER		0
> +#else
>   #define PMD_ORDER		aieeee_attempt_to_allocate_pmd
> +#endif
>   #define PTE_ORDER		0
>   #endif
>
> @@ -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)
>   #define FIRST_USER_ADDRESS	0UL
>
>   /*
> 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))
> +#else
> +#define TASK_SIZE64     (0x10000000000UL)
> +#endif
>   #define TASK_SIZE (test_thread_flag(TIF_32BIT_ADDR) ? TASK_SIZE32 : TASK_SIZE64)
>   #define STACK_TOP_MAX	TASK_SIZE64
>
>
> --
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