linux-kernel - Re: [PATCH 06/11] arm64: Move post_ttbr_update

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Date:   Thu, 4 Jan 2018 16:25:50 +0000
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Will Deacon <will.deacon@....com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <marc.zyngier@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 06/11] arm64: Move post_ttbr_update_workaround to C code

On 4 January 2018 at 15:08, Will Deacon <will.deacon@....com> wrote:
> From: Marc Zyngier <marc.zyngier@....com>
>
> We will soon need to invoke a CPU-specific function pointer after changing
> page tables, so move post_ttbr_update_workaround out into C code to make
> this possible.
>
> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> Signed-off-by: Will Deacon <will.deacon@....com>
> ---
>  arch/arm64/include/asm/assembler.h | 13 -------------
>  arch/arm64/kernel/entry.S          |  2 +-
>  arch/arm64/mm/context.c            |  9 +++++++++
>  arch/arm64/mm/proc.S               |  3 +--
>  4 files changed, 11 insertions(+), 16 deletions(-)
>
> diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
> index c45bc94f15d0..cee60ce0da52 100644
> --- a/arch/arm64/include/asm/assembler.h
> +++ b/arch/arm64/include/asm/assembler.h
> @@ -476,17 +476,4 @@ alternative_endif
>         mrs     \rd, sp_el0
>         .endm
>
> -/*
> - * Errata workaround post TTBRx_EL1 update.
> - */
> -       .macro  post_ttbr_update_workaround
> -#ifdef CONFIG_CAVIUM_ERRATUM_27456
> -alternative_if ARM64_WORKAROUND_CAVIUM_27456
> -       ic      iallu
> -       dsb     nsh
> -       isb
> -alternative_else_nop_endif
> -#endif
> -       .endm
> -
>  #endif /* __ASM_ASSEMBLER_H */
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index b9feb587294d..6aa112baf601 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -277,7 +277,7 @@ alternative_else_nop_endif
>          * Cavium erratum 27456 (broadcast TLBI instructions may cause I-cache
>          * corruption).
>          */
> -       post_ttbr_update_workaround
> +       bl      post_ttbr_update_workaround
>         .endif
>  1:
>         .if     \el != 0
> diff --git a/arch/arm64/mm/context.c b/arch/arm64/mm/context.c
> index 1cb3bc92ae5c..c1e3b6479c8f 100644
> --- a/arch/arm64/mm/context.c
> +++ b/arch/arm64/mm/context.c
> @@ -239,6 +239,15 @@ void check_and_switch_context(struct mm_struct *mm, unsigned int cpu)
>                 cpu_switch_mm(mm->pgd, mm);
>  }
>
> +/* Errata workaround post TTBRx_EL1 update. */
> +asmlinkage void post_ttbr_update_workaround(void)
> +{
> +       asm volatile(ALTERNATIVE("nop; nop; nop",

What does 'volatile' add here?

> +                                "ic iallu; dsb nsh; isb",
> +                                ARM64_WORKAROUND_CAVIUM_27456,
> +                                CONFIG_CAVIUM_ERRATUM_27456));
> +}
> +
>  static int asids_init(void)
>  {
>         asid_bits = get_cpu_asid_bits();
> diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
> index 3146dc96f05b..6affb68a9a14 100644
> --- a/arch/arm64/mm/proc.S
> +++ b/arch/arm64/mm/proc.S
> @@ -145,8 +145,7 @@ ENTRY(cpu_do_switch_mm)
>         isb
>         msr     ttbr0_el1, x0                   // now update TTBR0
>         isb
> -       post_ttbr_update_workaround
> -       ret
> +       b       post_ttbr_update_workaround     // Back to C code...
>  ENDPROC(cpu_do_switch_mm)
>
>         .pushsection ".idmap.text", "ax"
> --
> 2.1.4
>