Re: [PATCH v2 4/6] mm: replace vma->vm_flags indirect modification in ksm_madvise

[Mike Rapoport <rppt@xxxxxxxxxx>]

On Wed, Jan 25, 2023 at 12:38:49AM -0800, Suren Baghdasaryan wrote:
> Replace indirect modifications to vma->vm_flags with calls to modifier
> functions to be able to track flag changes and to keep vma locking
> correctness. Add a BUG_ON check in ksm_madvise() to catch indirect
> vm_flags modification attempts.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>

Acked-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>

> ---
>  arch/powerpc/kvm/book3s_hv_uvmem.c | 5 ++++-
>  arch/s390/mm/gmap.c                | 5 ++++-
>  mm/khugepaged.c                    | 2 ++
>  mm/ksm.c                           | 2 ++
>  4 files changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
> index 1d67baa5557a..325a7a47d348 100644
> --- a/arch/powerpc/kvm/book3s_hv_uvmem.c
> +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
> @@ -393,6 +393,7 @@ static int kvmppc_memslot_page_merge(struct kvm *kvm,
>  {
>  	unsigned long gfn = memslot->base_gfn;
>  	unsigned long end, start = gfn_to_hva(kvm, gfn);
> +	unsigned long vm_flags;
>  	int ret = 0;
>  	struct vm_area_struct *vma;
>  	int merge_flag = (merge) ? MADV_MERGEABLE : MADV_UNMERGEABLE;
> @@ -409,12 +410,14 @@ static int kvmppc_memslot_page_merge(struct kvm *kvm,
>  			ret = H_STATE;
>  			break;
>  		}
> +		vm_flags = vma->vm_flags;
>  		ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
> -			  merge_flag, &vma->vm_flags);
> +			  merge_flag, &vm_flags);
>  		if (ret) {
>  			ret = H_STATE;
>  			break;
>  		}
> +		reset_vm_flags(vma, vm_flags);
>  		start = vma->vm_end;
>  	} while (end > vma->vm_end);
>  
> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> index 3a695b8a1e3c..d5eb47dcdacb 100644
> --- a/arch/s390/mm/gmap.c
> +++ b/arch/s390/mm/gmap.c
> @@ -2587,14 +2587,17 @@ int gmap_mark_unmergeable(void)
>  {
>  	struct mm_struct *mm = current->mm;
>  	struct vm_area_struct *vma;
> +	unsigned long vm_flags;
>  	int ret;
>  	VMA_ITERATOR(vmi, mm, 0);
>  
>  	for_each_vma(vmi, vma) {
> +		vm_flags = vma->vm_flags;
>  		ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
> -				  MADV_UNMERGEABLE, &vma->vm_flags);
> +				  MADV_UNMERGEABLE, &vm_flags);
>  		if (ret)
>  			return ret;
> +		reset_vm_flags(vma, vm_flags);
>  	}
>  	mm->def_flags &= ~VM_MERGEABLE;
>  	return 0;
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 8abc59345bf2..76b24cd0c179 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -354,6 +354,8 @@ struct attribute_group khugepaged_attr_group = {
>  int hugepage_madvise(struct vm_area_struct *vma,
>  		     unsigned long *vm_flags, int advice)
>  {
> +	/* vma->vm_flags can be changed only using modifier functions */
> +	BUG_ON(vm_flags == &vma->vm_flags);
>  	switch (advice) {
>  	case MADV_HUGEPAGE:
>  #ifdef CONFIG_S390
> diff --git a/mm/ksm.c b/mm/ksm.c
> index 04f1c8c2df11..992b2be9f5e6 100644
> --- a/mm/ksm.c
> +++ b/mm/ksm.c
> @@ -2573,6 +2573,8 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
>  	struct mm_struct *mm = vma->vm_mm;
>  	int err;
>  
> +	/* vma->vm_flags can be changed only using modifier functions */
> +	BUG_ON(vm_flags == &vma->vm_flags);
>  	switch (advice) {
>  	case MADV_MERGEABLE:
>  		/*
> -- 
> 2.39.1
> 
>