[4/4] arm64/mm: Drop vm_fault_t argument from __do_page_fault()
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Message ID 1559133285-27986-5-git-send-email-anshuman.khandual@arm.com
State New
Headers show
Series
  • arm64/mm: Fixes and cleanups for do_page_fault()
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Commit Message

Anshuman Khandual May 29, 2019, 12:34 p.m. UTC
__do_page_fault() is over complicated with multiple goto statements. This
cleans up code flow and while there drops the vm_fault_t argument.

Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: James Morse <james.morse@arm.com> 
Cc: Andrey Konovalov <andreyknvl@google.com>
---
 arch/arm64/mm/fault.c | 38 ++++++++++++++++----------------------
 1 file changed, 16 insertions(+), 22 deletions(-)

Comments

Mark Rutland May 29, 2019, 3:11 p.m. UTC | #1
On Wed, May 29, 2019 at 06:04:45PM +0530, Anshuman Khandual wrote:
> __do_page_fault() is over complicated with multiple goto statements. This
> cleans up code flow and while there drops the vm_fault_t argument.
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: James Morse <james.morse@arm.com> 
> Cc: Andrey Konovalov <andreyknvl@google.com>
> ---
>  arch/arm64/mm/fault.c | 38 ++++++++++++++++----------------------
>  1 file changed, 16 insertions(+), 22 deletions(-)
> 
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 170c71f..a53a30e 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -397,37 +397,31 @@ 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.
> +	 * Check if the VMA has got the required permssion with respect
> +	 * to the access fault here.
>  	 */

We already had a perfectly good comment for this check:

	/*
	 * Check that the permissions on the VMA allow for the fault which
	 * occurred.
	 */

... so please keep that and minimize the diff.

> -good_area:
> +	if (!(vma->vm_flags & vm_flags))
> +		return VM_FAULT_BADACCESS;
> +
>  	/*
> -	 * Check that the permissions on the VMA allow for the fault which
> -	 * occurred.
> +	 * There is a valid VMA for this access. But before proceeding
> +	 * make sure that it has required flags if there is an attempt
> +	 * to expand the stack downwards.
>  	 */

I think we can drop this comment, given we didn't have it previously.

> -	if (!(vma->vm_flags & vm_flags)) {
> -		fault = VM_FAULT_BADACCESS;
> -		goto out;
> -	}
> +	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;

You can drop the line space between these two if statements.

> +	}
>  	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;

We used to check the stack before the checknig the rest of the vm_flags,
so this changes the precedence of the VM_FAULT_BADMAP and
VM_FAULT_BADACCESS return codes.

Please check the stack before checking the other vm_flags.

Otherwise, this looks like a nice cleanup -- the old control flow was
hideous.

Thanks,
Mark.
Christoph Hellwig May 30, 2019, 6:34 a.m. UTC | #2
On Wed, May 29, 2019 at 06:04:45PM +0530, Anshuman Khandual wrote:
> __do_page_fault() is over complicated with multiple goto statements. This
> cleans up code flow and while there drops the vm_fault_t argument.

There is no argument dropped anywhere, just a local variable.
Anshuman Khandual May 31, 2019, 8:55 a.m. UTC | #3
On 05/30/2019 12:04 PM, Christoph Hellwig wrote:
> On Wed, May 29, 2019 at 06:04:45PM +0530, Anshuman Khandual wrote:
>> __do_page_fault() is over complicated with multiple goto statements. This
>> cleans up code flow and while there drops the vm_fault_t argument.
> 
> There is no argument dropped anywhere, just a local variable.
> 

You are right. Will fix both subject line and the commit message.
Anshuman Khandual May 31, 2019, 9:05 a.m. UTC | #4
On 05/29/2019 08:41 PM, Mark Rutland wrote:
> On Wed, May 29, 2019 at 06:04:45PM +0530, Anshuman Khandual wrote:
>> __do_page_fault() is over complicated with multiple goto statements. This
>> cleans up code flow and while there drops the vm_fault_t argument.
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
>>
>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Will Deacon <will.deacon@arm.com>
>> Cc: Mark Rutland <mark.rutland@arm.com>
>> Cc: James Morse <james.morse@arm.com> 
>> Cc: Andrey Konovalov <andreyknvl@google.com>
>> ---
>>  arch/arm64/mm/fault.c | 38 ++++++++++++++++----------------------
>>  1 file changed, 16 insertions(+), 22 deletions(-)
>>
>> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
>> index 170c71f..a53a30e 100644
>> --- a/arch/arm64/mm/fault.c
>> +++ b/arch/arm64/mm/fault.c
>> @@ -397,37 +397,31 @@ 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.
>> +	 * Check if the VMA has got the required permssion with respect
>> +	 * to the access fault here.
>>  	 */
> 
> We already had a perfectly good comment for this check:
> 
> 	/*
> 	 * Check that the permissions on the VMA allow for the fault which
> 	 * occurred.
> 	 */
> 
> ... so please keep that and minimize the diff.

Sure, will keep all the existing comments here.

> 
>> -good_area:
>> +	if (!(vma->vm_flags & vm_flags))
>> +		return VM_FAULT_BADACCESS;
>> +
>>  	/*
>> -	 * Check that the permissions on the VMA allow for the fault which
>> -	 * occurred.
>> +	 * There is a valid VMA for this access. But before proceeding
>> +	 * make sure that it has required flags if there is an attempt
>> +	 * to expand the stack downwards.
>>  	 */
> 
> I think we can drop this comment, given we didn't have it previously.

Okay.

> 
>> -	if (!(vma->vm_flags & vm_flags)) {
>> -		fault = VM_FAULT_BADACCESS;
>> -		goto out;
>> -	}
>> +	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;
> 
> You can drop the line space between these two if statements.

Will do.

> 
>> +	}
>>  	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;
> 
> We used to check the stack before the checknig the rest of the vm_flags,
> so this changes the precedence of the VM_FAULT_BADMAP and
> VM_FAULT_BADACCESS return codes.
> 
> Please check the stack before checking the other vm_flags.

Though it makes some sense to move VMA permission check earlier in the function as it
is the quicker one but I understand need to maintain the existing code flow in a clean
up patch like this. Will retain the existing flow.

Patch
diff mbox series

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 170c71f..a53a30e 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -397,37 +397,31 @@  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.
+	 * Check if the VMA has got the required permssion with respect
+	 * to the access fault here.
 	 */
-good_area:
+	if (!(vma->vm_flags & vm_flags))
+		return VM_FAULT_BADACCESS;
+
 	/*
-	 * Check that the permissions on the VMA allow for the fault which
-	 * occurred.
+	 * There is a valid VMA for this access. But before proceeding
+	 * make sure that it has required flags if there is an attempt
+	 * to expand the stack downwards.
 	 */
-	if (!(vma->vm_flags & vm_flags)) {
-		fault = VM_FAULT_BADACCESS;
-		goto out;
-	}
+	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;
+	}
 	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)