linux-kernel - Re: [v4,17/21] powerpc/8xx: set PTE bit 22 off TLBmiss

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Date:	Thu, 6 Nov 2014 21:37:45 -0600
From:	Scott Wood <scottwood@...escale.com>
To:	LEROY Christophe <christophe.leroy@....fr>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	<linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [v4,17/21] powerpc/8xx: set PTE bit 22 off TLBmiss

On Fri, Sep 19, 2014 at 10:36:09AM +0200, LEROY Christophe wrote:
> No need to re-set this bit at each TLB miss. Let's set it in the PTE.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> ---
> Changes in v2:
> - None
> 
> Changes in v3:
> - Removed PPC405 related macro from PPC8xx specific code
> - PTE_NONE_MASK doesn't need PAGE_ACCESSED in Linux 2.6
> 
> Changes in v4:
> - None
> 
>  arch/powerpc/include/asm/pgtable-ppc32.h | 20 ++++++++++++++++++++
>  arch/powerpc/include/asm/pte-8xx.h       |  7 +++++--
>  arch/powerpc/kernel/head_8xx.S           | 10 ++--------
>  3 files changed, 27 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/pgtable-ppc32.h b/arch/powerpc/include/asm/pgtable-ppc32.h
> index 47edde8..35a9b44 100644
> --- a/arch/powerpc/include/asm/pgtable-ppc32.h
> +++ b/arch/powerpc/include/asm/pgtable-ppc32.h
> @@ -172,6 +172,25 @@ static inline unsigned long pte_update(pte_t *p,
>  #ifdef PTE_ATOMIC_UPDATES
>  	unsigned long old, tmp;
>  
> +#ifdef CONFIG_PPC_8xx
> +	unsigned long tmp2;
> +
> +	__asm__ __volatile__("\
> +1:	lwarx	%0,0,%4\n\
> +	andc	%1,%0,%5\n\
> +	or	%1,%1,%6\n\
> +	/* 0x200 == Extended encoding, bit 22 */ \
> +	/* Bit 22 has to be 1 if neither _PAGE_USER nor _PAGE_RW are set */ \
> +	rlwimi	%1,%1,32-2,0x200\n /* get _PAGE_USER */ \
> +	rlwinm	%3,%1,32-1,0x200\n /* get _PAGE_RW */ \
> +	or	%1,%3,%1\n\
> +	xori	%1,%1,0x200\n"
> +"	stwcx.	%1,0,%4\n\
> +	bne-	1b"

Why do you need this...

> diff --git a/arch/powerpc/include/asm/pte-8xx.h b/arch/powerpc/include/asm/pte-8xx.h
> index d44826e..daa4616 100644
> --- a/arch/powerpc/include/asm/pte-8xx.h
> +++ b/arch/powerpc/include/asm/pte-8xx.h
> @@ -48,19 +48,22 @@
>   */
>  #define _PAGE_RW	0x0400	/* lsb PP bits, inverted in HW */
>  #define _PAGE_USER	0x0800	/* msb PP bits */
> +/* set when neither _PAGE_USER nor _PAGE_RW are set */
> +#define _PAGE_KNLRO	0x0200
>  
>  #define _PMD_PRESENT	0x0001
>  #define _PMD_BAD	0x0ff0
>  #define _PMD_PAGE_MASK	0x000c
>  #define _PMD_PAGE_8M	0x000c
>  
> -#define _PTE_NONE_MASK _PAGE_ACCESSED
> +#define _PTE_NONE_MASK _PAGE_KNLRO
>  
>  /* Until my rework is finished, 8xx still needs atomic PTE updates */
>  #define PTE_ATOMIC_UPDATES	1
>  
>  /* We need to add _PAGE_SHARED to kernel pages */
> -#define _PAGE_KERNEL_RO	(_PAGE_SHARED)
> +#define _PAGE_KERNEL_RO	(_PAGE_SHARED | _PAGE_KNLRO)
> +#define _PAGE_KERNEL_ROX	(_PAGE_EXEC | _PAGE_KNLRO)
>  #define _PAGE_KERNEL_RW	(_PAGE_DIRTY | _PAGE_RW | _PAGE_HWWRITE)

...if 0x200 is already being set in the PTE here?

-Scott
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