linux-kernel - Re: [PATCH 02/11] powerpc/8xx: remove tests on PGDIR entry validity

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Message-ID: <1420481741.25047.17.camel@transmode.se>
Date:	Mon, 5 Jan 2015 18:15:40 +0000
From:	Joakim Tjernlund <Joakim.Tjernlund@...nsmode.se>
To:	"christophe.leroy@....fr" <christophe.leroy@....fr>
CC:	"scottwood@...escale.com" <scottwood@...escale.com>,
	"paulus@...ba.org" <paulus@...ba.org>,
	"mpe@...erman.id.au" <mpe@...erman.id.au>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 02/11] powerpc/8xx: remove tests on PGDIR entry validity


On Tue, 2014-12-16 at 16:03 +0100, Christophe Leroy wrote:
> Kernel MMU handling code handles validity of entries via _PMD_PRESENT which
> corresponds to V bit in MD_TWC and MI_TWC. When the V bit is not set, MPC8xx
> triggers TLBError exception. So we don't have to check that and branch ourself
> to TLBError. We can set TLB entries with non present entries, remove all those
> tests and let the 8xx handle it. This reduce the number of cycle when the
> entries are valid which is the case most of the time, and doesn't significantly
> increase the time for handling invalid entries.
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>

Nice :)
Acked-by: Joakim Tjernlund <joakim.tjernlund@...nsmode.se>

> 
> ---
>  arch/powerpc/kernel/head_8xx.S | 41 ++++++++---------------------------------
>  1 file changed, 8 insertions(+), 33 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
> index 79b8a23..2c329f1 100644
> --- a/arch/powerpc/kernel/head_8xx.S
> +++ b/arch/powerpc/kernel/head_8xx.S
> @@ -329,12 +329,9 @@ InstructionTLBMiss:
>         /* Extract level 1 index */
>         rlwinm  r10, r10, 32 - ((PAGE_SHIFT - 2) << 1), (PAGE_SHIFT - 2) << 1, 29
>         lwzx    r11, r10, r11/* Get the level 1 entry */
> -       rlwinm. r10, r11,0,0,19/* Extract page descriptor page address */
> -       beq     2f      /* If zero, don't try to find a pte */
> +       rlwinm  r10, r11,0,0,19/* Extract page descriptor page address */
>  
> -       /* We have a pte table, so load the MI_TWC with the attributes
> -               * for this "segment."
> -               */
> +       /* Load the MI_TWC with the attributes for this "segment." */
>         MTSPR_CPU6(SPRN_MI_TWC, r11, r3)/* Set segment attributes */
>         mfspr   r11, SPRN_SRR0/* Get effective address of fault */
>         /* Extract level 2 index */
> @@ -342,13 +339,11 @@ InstructionTLBMiss:
>         lwzx    r10, r10, r11/* Get the pte */
>  
>  #ifdef CONFIG_SWAP
> -       andi.   r11, r10, _PAGE_ACCESSED | _PAGE_PRESENT
> -       cmpwi   cr0, r11, _PAGE_ACCESSED | _PAGE_PRESENT
> -       li      r11, RPN_PATTERN
> -       bne-    cr0, 2f
> -#else
> -       li      r11, RPN_PATTERN
> +       rlwinm  r11, r10, 32-5, _PAGE_PRESENT
> +       and     r11, r11, r10
> +       rlwimi  r10, r11, 0, _PAGE_PRESENT
>  #endif
> +       li      r11, RPN_PATTERN
>         /* The Linux PTE won't go exactly into the MMU TLB.
>                 * Software indicator bits 21 and 28 must be clear.
>                 * Software indicator bits 24, 25, 26, and 27 must be
> @@ -366,21 +361,6 @@ InstructionTLBMiss:
>         mfspr   r10, SPRN_SPRG_SCRATCH2
>         EXCEPTION_EPILOG_0
>         rfi
> -2:
> -       mfspr   r10, SPRN_SRR1
> -       /* clear all error bits as TLB Miss
> -               * sets a few unconditionally
> -       */
> -       rlwinm  r10, r10, 0, 0xffff
> -       mtspr   SPRN_SRR1, r10
> -
> -       /* Restore registers */
> -#ifdef CONFIG_8xx_CPU6
> -       mfspr   r3, SPRN_DAR
> -       mtspr   SPRN_DAR, r11/* Tag DAR */
> -#endif
> -       mfspr   r10, SPRN_SPRG_SCRATCH2
> -       b       InstructionTLBError1
>  
>         . = 0x1200
>  DataStoreTLBMiss:
> @@ -403,8 +383,6 @@ DataStoreTLBMiss:
>         /* Extract level 1 index */
>         rlwinm  r10, r10, 32 - ((PAGE_SHIFT - 2) << 1), (PAGE_SHIFT - 2) << 1, 29
>         lwzx    r11, r10, r11/* Get the level 1 entry */
> -       rlwinm. r10, r11,0,0,19/* Extract page descriptor page address */
> -       beq     2f      /* If zero, don't try to find a pte */
>  
>         /* We have a pte table, so load fetch the pte from the table.
>                 */
> @@ -450,7 +428,7 @@ DataStoreTLBMiss:
>                 * set.  All other Linux PTE bits control the behavior
>                 * of the MMU.
>                 */
> -2:     li      r11, RPN_PATTERN
> +       li      r11, RPN_PATTERN
>         rlwimi  r10, r11, 0, 24, 28/* Set 24-27, clear 28 */
>         MTSPR_CPU6(SPRN_MD_RPN, r10, r3)/* Update TLB entry */
>  
> @@ -469,10 +447,7 @@ DataStoreTLBMiss:
>   */
>         . = 0x1300
>  InstructionTLBError:
> -       EXCEPTION_PROLOG_0
> -InstructionTLBError1:
> -       EXCEPTION_PROLOG_1
> -       EXCEPTION_PROLOG_2
> +       EXCEPTION_PROLOG
>         mr      r4,r12
>         mr      r5,r9
>         andis.  r10,r5,0x4000--
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