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Re: [PATCH] MIPS: Add missing hazard barrier in TLB load handler.

To: "Steven J. Hill" <Steven.Hill@imgtec.com>
Subject: Re: [PATCH] MIPS: Add missing hazard barrier in TLB load handler.
From: Ralf Baechle <ralf@linux-mips.org>
Date: Thu, 20 Jun 2013 13:07:38 +0200
Cc: linux-mips@linux-mips.org, Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
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On Thu, Jun 20, 2013 at 12:57:54AM -0500, Steven J. Hill wrote:

> MIPS R2 documents state that an execution hazard barrier is needed
> after a TLBR before reading EntryLo.
> 
> Change-Id: Idef3b6abbb63a1bbd5e153c6110a979fa7bd5896
> Signed-off-by: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
> Acked-by: Steven J. Hill <Steven.Hill@imgtec.com>
> ---
>  arch/mips/mm/tlbex.c |   10 ++++++++++
>  1 files changed, 10 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/mips/mm/tlbex.c b/arch/mips/mm/tlbex.c
> index d9969d2..5ef426c 100644
> --- a/arch/mips/mm/tlbex.c
> +++ b/arch/mips/mm/tlbex.c
> @@ -1922,6 +1922,11 @@ static void build_r4000_tlb_load_handler(void)
>               uasm_i_nop(&p);
>  
>               uasm_i_tlbr(&p);
> +#if !defined(CONFIG_CPU_CAVIUM_OCTEON)
> +             /* hazard barrier after TLBR but before read EntryLo */
> +             if (cpu_has_mips_r2)
> +                     uasm_i_ehb(&p);
> +#endif
>               /* Examine  entrylo 0 or 1 based on ptr. */
>               if (use_bbit_insns()) {
>                       uasm_i_bbit0(&p, wr.r2, ilog2(sizeof(pte_t)), 8);
> @@ -1976,6 +1981,11 @@ static void build_r4000_tlb_load_handler(void)
>               uasm_i_nop(&p);
>  
>               uasm_i_tlbr(&p);
> +#if !defined(CONFIG_CPU_CAVIUM_OCTEON)
> +             /* hazard barrier after TLBR but before read EntryLo */
> +             if (cpu_has_mips_r2)
> +                     uasm_i_ehb(&p);
> +#endif
>               /* Examine  entrylo 0 or 1 based on ptr. */
>               if (use_bbit_insns()) {
>                       uasm_i_bbit0(&p, wr.r2, ilog2(sizeof(pte_t)), 8);

And guess which lines the sulphur smell in this patch is coming from.

  Ralf

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