linux-kernel - Re: [PATCH V2 2/2] arm64: errata: Workaround possible Cortex-A715 [ESR|FAR]

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Date:   Wed, 16 Nov 2022 09:00:12 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        will@...nel.org, Suzuki K Poulose <suzuki.poulose@....com>,
        James Morse <james.morse@....com>,
        Jonathan Corbet <corbet@....net>,
        Mark Rutland <mark.rutland@....com>, linux-doc@...r.kernel.org
Subject: Re: [PATCH V2 2/2] arm64: errata: Workaround possible Cortex-A715
 [ESR|FAR]_ELx corruption

On Wed, Nov 16, 2022 at 10:12:34AM +0530, Anshuman Khandual wrote:
> Planning to apply the following change after this patch.
> 
> diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
> index 6552947ca7fa..cd8d96e1fa1a 100644
> --- a/arch/arm64/mm/hugetlbpage.c
> +++ b/arch/arm64/mm/hugetlbpage.c
> @@ -562,14 +562,14 @@ bool __init arch_hugetlb_valid_size(unsigned long size)
>  
>  pte_t huge_ptep_modify_prot_start(struct vm_area_struct *vma, unsigned long addr, pte_t *ptep)
>  {
> -       if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198)) {
> -               pte_t pte = READ_ONCE(*ptep);
> +       if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198) &&
> +           cpus_have_const_cap(ARM64_WORKAROUND_2645198)) {
>                 /*
>                  * Break-before-make (BBM) is required for all user space mappings
>                  * when the permission changes from executable to non-executable
>                  * in cases where cpu is affected with errata #2645198.
>                  */
> -               if (pte_user_exec(pte) && cpus_have_const_cap(ARM64_WORKAROUND_2645198))
> +               if (pte_user_exec(READ_ONCE(*ptep)))
>                         return huge_ptep_clear_flush(vma, addr, ptep);
>         }
>         return huge_ptep_get_and_clear(vma->vm_mm, addr, ptep);
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index c1fb0ce1473c..ec305ea3942c 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1705,14 +1705,14 @@ early_initcall(prevent_bootmem_remove_init);
>  
>  pte_t ptep_modify_prot_start(struct vm_area_struct *vma, unsigned long addr, pte_t *ptep)
>  {
> -       if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198)) {
> -               pte_t pte = READ_ONCE(*ptep);
> +       if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198) &&
> +           cpus_have_const_cap(ARM64_WORKAROUND_2645198)) {
>                 /*
>                  * Break-before-make (BBM) is required for all user space mappings
>                  * when the permission changes from executable to non-executable
>                  * in cases where cpu is affected with errata #2645198.
>                  */
> -               if (pte_user_exec(pte) && cpus_have_const_cap(ARM64_WORKAROUND_2645198))
> +               if (pte_user_exec(READ_ONCE(*ptep)))
>                         return ptep_clear_flush(vma, addr, ptep);
>         }
>         return ptep_get_and_clear(vma->vm_mm, addr, ptep);

It looks fine to me. Thanks.

-- 
Catalin