linux-kernel - Re: [PATCH v2 17/19] powerpc/8xx: set PTE bit 22 off TLBmiss

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Message-ID: <OFC266DD00.56C086CA-ONC1257D43.005005B3-C1257D43.00508E4E@transmode.se>
Date:	Fri, 29 Aug 2014 16:39:52 +0200
From:	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
To:	Christophe Leroy <christophe.leroy@....fr>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	Paul Mackerras <paulus@...ba.org>, scottwood@...escale.com
Subject: Re: [PATCH v2 17/19] powerpc/8xx: set PTE bit 22 off TLBmiss

Christophe Leroy <christophe.leroy@....fr> wrote on 2014/08/29 11:14:40:
> 
> 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>
> 
> ---
>  arch/powerpc/include/asm/pgtable-ppc32.h |   21 +++++++++++++++++++++
>  arch/powerpc/include/asm/pte-8xx.h       |    7 +++++--
>  arch/powerpc/kernel/head_8xx.S           |   10 ++--------
>  3 files changed, 28 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/pgtable-ppc32.h 
b/arch/powerpc/include/asm/pgtable-ppc32.h
> index 47edde8..c261792 100644
> --- a/arch/powerpc/include/asm/pgtable-ppc32.h
> +++ b/arch/powerpc/include/asm/pgtable-ppc32.h
> @@ -172,6 +172,26 @@ 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"
> +   PPC405_ERR77(0,%4)

Should above PPC405_XXXX really be there? This is 8xx only

> +"   stwcx.   %1,0,%4\n\
> +   bne-   1b"
> +   : "=&r" (old), "=&r" (tmp), "=m" (*p), "=&r" (tmp2)
> +   : "r" (p), "r" (clr), "r" (set), "m" (*p)
> +   : "cc" );
> +#else /* CONFIG_PPC_8xx */
>     __asm__ __volatile__("\
>  1:   lwarx   %0,0,%3\n\
>     andc   %1,%0,%4\n\
> @@ -182,6 +202,7 @@ static inline unsigned long pte_update(pte_t *p,
>     : "=&r" (old), "=&r" (tmp), "=m" (*p)
>     : "r" (p), "r" (clr), "r" (set), "m" (*p)
>     : "cc" );
> +#endif /* CONFIG_PPC_8xx */
>  #else /* PTE_ATOMIC_UPDATES */
>     unsigned long old = pte_val(*p);
>     *p = __pte((old & ~clr) | set);
> diff --git a/arch/powerpc/include/asm/pte-8xx.h 
b/arch/powerpc/include/asm/pte-8xx.h
> index d44826e..dede1e7 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_ACCESSED | _PAGE_KNLRO)

_PAGE_ACCESSED can be removed from PTE_NONE_MASK as 8xx no longer cheets.
See 2.4 commit 
https://git.kernel.org/cgit/linux/kernel/git/wtarreau/linux-2.4.git/commit/?id=82582b970d04ad4bcfaa9d3f9c3c256619fd889f

> 
>  /* 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)
> 
>  #endif /* __KERNEL__ */
> diff --git a/arch/powerpc/kernel/head_8xx.S 
b/arch/powerpc/kernel/head_8xx.S
> index a7af26e..48d3de8 100644
> --- a/arch/powerpc/kernel/head_8xx.S
> +++ b/arch/powerpc/kernel/head_8xx.S
> @@ -445,14 +445,8 @@ DataStoreTLBMiss:
>     and   r11, r11, r10
>     rlwimi   r10, r11, 0, _PAGE_PRESENT
>  #endif
> -   /* Honour kernel RO, User NA */
> -   /* 0x200 == Extended encoding, bit 22 */
> -   rlwimi   r10, r10, 32-2, 0x200 /* Copy USER to bit 22, 0x200 */
> -   /* r11 =  (r10 & _PAGE_RW) >> 1 */
> -   rlwinm   r11, r10, 32-1, 0x200
> -   or   r10, r11, r10
> -   /* invert RW and 0x200 bits */
> -   xori   r10, r10, _PAGE_RW | 0x200
> +   /* invert RW */
> +   xori   r10, r10, _PAGE_RW
> 
>     /* The Linux PTE won't go exactly into the MMU TLB.
>      * Software indicator bits 22 and 28 must be clear.
> -- 
> 1.7.1
> 

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