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

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Message-ID: <Y3Ob2MmmuoXOs2In@arm.com>
Date:   Tue, 15 Nov 2022 14:02:00 +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 Sun, Nov 13, 2022 at 06:56:45AM +0530, Anshuman Khandual wrote:
> diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
> index 35e9a468d13e..6552947ca7fa 100644
> --- a/arch/arm64/mm/hugetlbpage.c
> +++ b/arch/arm64/mm/hugetlbpage.c
> @@ -559,3 +559,24 @@ bool __init arch_hugetlb_valid_size(unsigned long size)
>  {
>  	return __hugetlb_valid_size(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);

Not sure whether the generated code would be any different but we should
probably add the check for the CPU capability in the 'if' condition
above, before the READ_ONCE (which expands to some asm volatile):

	if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198) &&
	    cpus_have_const_cap(ARM64_WORKAROUND_2645198)) {
		pte_t pte = ...
		...
	}

> +		/*
> +		 * 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))
> +			return huge_ptep_clear_flush(vma, addr, ptep);
> +	}
> +	return huge_ptep_get_and_clear(vma->vm_mm, addr, ptep);
> +}
> +
> +void huge_ptep_modify_prot_commit(struct vm_area_struct *vma, unsigned long addr, pte_t *ptep,
> +				  pte_t old_pte, pte_t pte)
> +{
> +	set_huge_pte_at(vma->vm_mm, addr, ptep, pte);
> +}
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 9a7c38965154..c1fb0ce1473c 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1702,3 +1702,24 @@ static int __init prevent_bootmem_remove_init(void)
>  }
>  early_initcall(prevent_bootmem_remove_init);
>  #endif
> +
> +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);
> +		/*
> +		 * 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))
> +			return ptep_clear_flush(vma, addr, ptep);
> +	}

Same here.

> +	return ptep_get_and_clear(vma->vm_mm, addr, ptep);
> +}
> +
> +void ptep_modify_prot_commit(struct vm_area_struct *vma, unsigned long addr, pte_t *ptep,
> +			     pte_t old_pte, pte_t pte)
> +{
> +	__set_pte_at(vma->vm_mm, addr, ptep, pte);
> +}

-- 
Catalin