Re: [PATCH 4/4] arm64/mm: Drop vm_fault_t argument from __do_page_fault()
From: Mark Rutland <mark.rutland@arm.com>
Date: 2019-05-29 15:11:41
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On Wed, May 29, 2019 at 06:04:45PM +0530, Anshuman Khandual wrote:
quoted hunk ↗ jump to hunk
__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 <redacted> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <redacted> Cc: Mark Rutland <mark.rutland@arm.com> Cc: James Morse <james.morse@arm.com> Cc: Andrey Konovalov <redacted> --- 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. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel