[RFC PATCH RESEND 09/28] mm/mempolicy: mark VMA as locked when changing protection policy

[Laurent Dufour]

Le 01/09/2022 à 19:34, Suren Baghdasaryan a écrit :
> Protect VMA from concurrent page fault handler while performing VMA
> protection policy changes.
> 
> Signed-off-by: Suren Baghdasaryan <surenb at google.com>
> ---
>  mm/mempolicy.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index b73d3248d976..6be1e5c75556 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -383,8 +383,10 @@ void mpol_rebind_mm(struct mm_struct *mm, nodemask_t *new)
>  	struct vm_area_struct *vma;
>  
>  	mmap_write_lock(mm);
> -	for (vma = mm->mmap; vma; vma = vma->vm_next)
> +	for (vma = mm->mmap; vma; vma = vma->vm_next) {
> +		vma_mark_locked(vma);
>  		mpol_rebind_policy(vma->vm_policy, new);
> +	}
>  	mmap_write_unlock(mm);
>  }
>  
> @@ -632,6 +634,7 @@ unsigned long change_prot_numa(struct vm_area_struct *vma,
>  	struct mmu_gather tlb;
>  	int nr_updated;
>  
> +	vma_mark_locked(vma);

If I understand that corretly, the VMA itself is not impacted, only the
PMDs/PTEs, and they are protected using the page table locks.

Am I missing something?

>  	tlb_gather_mmu(&tlb, vma->vm_mm);
>  
>  	nr_updated = change_protection(&tlb, vma, addr, end, PAGE_NONE,
> @@ -765,6 +768,7 @@ static int vma_replace_policy(struct vm_area_struct *vma,
>  	if (IS_ERR(new))
>  		return PTR_ERR(new);
>  
> +	vma_mark_locked(vma);
>  	if (vma->vm_ops && vma->vm_ops->set_policy) {
>  		err = vma->vm_ops->set_policy(vma, new);
>  		if (err)