linux-kernel - Re: [PATCH V3 2/2] arm64/mm: Refactor __do_page

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Date:   Fri, 7 Jun 2019 11:23:11 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        James Morse <james.morse@....com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH V3 2/2] arm64/mm: Refactor __do_page_fault()

On Fri, Jun 07, 2019 at 02:43:06PM +0530, Anshuman Khandual wrote:
> __do_page_fault() is over complicated with multiple goto statements. This
> cleans up the code flow and while there drops local variable vm_fault_t.
> 
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: James Morse <james.morse@....com>
> Cc: Andrey Konovalov <andreyknvl@...gle.com>
> Cc: Christoph Hellwig <hch@...radead.org>

This keeps the existing behaviour, and is certainly cleaner, so:

Reviewed-by: Mark Rutland <Mark.rutland@....com>

Mark.

> ---
>  arch/arm64/mm/fault.c | 30 +++++++++++-------------------
>  1 file changed, 11 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 95cac4a..235b7c0 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -397,37 +397,29 @@ static void do_bad_area(unsigned long addr, unsigned int esr, struct pt_regs *re
>  static vm_fault_t __do_page_fault(struct mm_struct *mm, unsigned long addr,
>  			   unsigned int mm_flags, unsigned long vm_flags)
>  {
> -	struct vm_area_struct *vma;
> -	vm_fault_t fault;
> +	struct vm_area_struct *vma = find_vma(mm, addr);
>  
> -	vma = find_vma(mm, addr);
> -	fault = VM_FAULT_BADMAP;
>  	if (unlikely(!vma))
> -		goto out;
> -	if (unlikely(vma->vm_start > addr))
> -		goto check_stack;
> +		return VM_FAULT_BADMAP;
>  
>  	/*
>  	 * Ok, we have a good vm_area for this memory access, so we can handle
>  	 * it.
>  	 */
> -good_area:
> +	if (unlikely(vma->vm_start > addr)) {
> +		if (!(vma->vm_flags & VM_GROWSDOWN))
> +			return VM_FAULT_BADMAP;
> +		if (expand_stack(vma, addr))
> +			return VM_FAULT_BADMAP;
> +	}
> +
>  	/*
>  	 * Check that the permissions on the VMA allow for the fault which
>  	 * occurred.
>  	 */
> -	if (!(vma->vm_flags & vm_flags)) {
> -		fault = VM_FAULT_BADACCESS;
> -		goto out;
> -	}
> -
> +	if (!(vma->vm_flags & vm_flags))
> +		return VM_FAULT_BADACCESS;
>  	return handle_mm_fault(vma, addr & PAGE_MASK, mm_flags);
> -
> -check_stack:
> -	if (vma->vm_flags & VM_GROWSDOWN && !expand_stack(vma, addr))
> -		goto good_area;
> -out:
> -	return fault;
>  }
>  
>  static bool is_el0_instruction_abort(unsigned int esr)
> -- 
> 2.7.4
>