linux-kernel - Re: [PATCH] mm/shmem: Zero out unused vma fields in shmem_pseudo_vma

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Date:   Thu, 31 May 2018 15:52:56 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/shmem: Zero out unused vma fields in
 shmem_pseudo_vma_init()

On Thu, 31 May 2018 16:56:02 +0300 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com> wrote:

> shmem/tmpfs uses pseudo vma to allocate page with correct NUMA policy.
> 
> The pseudo vma doesn't have vm_page_prot set. We are going to encode
> encryption KeyID in vm_page_prot. Having garbage there causes problems.
> 
> Zero out all unused fields in the pseudo vma.
> 

So there are no known problems in the current mainline kernel?

> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1404,10 +1404,9 @@ static void shmem_pseudo_vma_init(struct vm_area_struct *vma,
>  		struct shmem_inode_info *info, pgoff_t index)
>  {
>  	/* Create a pseudo vma that just contains the policy */
> -	vma->vm_start = 0;
> +	memset(vma, 0, sizeof(*vma));
>  	/* Bias interleave by inode number to distribute better across nodes */
>  	vma->vm_pgoff = index + info->vfs_inode.i_ino;
> -	vma->vm_ops = NULL;
>  	vma->vm_policy = mpol_shared_policy_lookup(&info->policy, index);
>  }