linux-kernel - Re: [PATCH] powerpc/8xx: drop unused self-modifying code alternative to FixupDAR.

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Message-ID: <c358a18b99a59ff600f83dd0c83ad80072f3d10b.camel@infinera.com>
Date:   Thu, 22 Aug 2019 07:05:57 +0000
From:   Joakim Tjernlund <Joakim.Tjernlund@...inera.com>
To:     "christophe.leroy@....fr" <christophe.leroy@....fr>,
        "paulus@...ba.org" <paulus@...ba.org>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>,
        "benh@...nel.crashing.org" <benh@...nel.crashing.org>
CC:     "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] powerpc/8xx: drop unused self-modifying code alternative
 to FixupDAR.

On Wed, 2019-08-21 at 20:00 +0000, Christophe Leroy wrote:
> 
> The code which fixups the DAR on TLB errors for dbcX instructions
> has a self-modifying code alternative that has never been used.
> 
> Drop it.

Argh, my master piece from way back :)
But it is time for it to go.

Reviewed-by: Joakim Tjernlund <joakim.tjernlund@...inera.com>

 Jocke
> 
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> ---
>  arch/powerpc/kernel/head_8xx.S | 24 ------------------------
>  1 file changed, 24 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
> index b8ca5b43e587..19f583e18402 100644
> --- a/arch/powerpc/kernel/head_8xx.S
> +++ b/arch/powerpc/kernel/head_8xx.S
> @@ -575,8 +575,6 @@ InstructionBreakpoint:
>   * by decoding the registers used by the dcbx instruction and adding them.
>   * DAR is set to the calculated address.
>   */
> - /* define if you don't want to use self modifying code */
> -#define NO_SELF_MODIFYING_CODE
>  FixupDAR:/* Entry point for dcbx workaround. */
>         mtspr   SPRN_M_TW, r10
>         /* fetch instruction from memory. */
> @@ -640,27 +638,6 @@ FixupDAR:/* Entry point for dcbx workaround. */
>         rlwinm  r10, r10,0,7,5  /* Clear store bit for buggy dcbst insn */
>         mtspr   SPRN_DSISR, r10
>  142:   /* continue, it was a dcbx, dcbi instruction. */
> -#ifndef NO_SELF_MODIFYING_CODE
> -       andis.  r10,r11,0x1f    /* test if reg RA is r0 */
> -       li      r10,modified_instr@l
> -       dcbtst  r0,r10          /* touch for store */
> -       rlwinm  r11,r11,0,0,20  /* Zero lower 10 bits */
> -       oris    r11,r11,640     /* Transform instr. to a "add r10,RA,RB" */
> -       ori     r11,r11,532
> -       stw     r11,0(r10)      /* store add/and instruction */
> -       dcbf    0,r10           /* flush new instr. to memory. */
> -       icbi    0,r10           /* invalidate instr. cache line */
> -       mfspr   r11, SPRN_SPRG_SCRATCH1 /* restore r11 */
> -       mfspr   r10, SPRN_SPRG_SCRATCH0 /* restore r10 */
> -       isync                   /* Wait until new instr is loaded from memory */
> -modified_instr:
> -       .space  4               /* this is where the add instr. is stored */
> -       bne+    143f
> -       subf    r10,r0,r10      /* r10=r10-r0, only if reg RA is r0 */
> -143:   mtdar   r10             /* store faulting EA in DAR */
> -       mfspr   r10,SPRN_M_TW
> -       b       DARFixed        /* Go back to normal TLB handling */
> -#else
>         mfctr   r10
>         mtdar   r10                     /* save ctr reg in DAR */
>         rlwinm  r10, r11, 24, 24, 28    /* offset into jump table for reg RB */
> @@ -724,7 +701,6 @@ modified_instr:
>         add     r10, r10, r11   /* add it */
>         mfctr   r11             /* restore r11 */
>         b       151b
> -#endif
> 
>  /*
>   * This is where the main kernel code starts.
> --
> 2.13.3
>