linux-kernel - Re: [PATCH v2 19/26] userfaultfd: introduce helper vma_find

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Date:   Thu, 21 Feb 2019 13:19:32 -0500
From:   Jerome Glisse <jglisse@...hat.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        David Hildenbrand <david@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Maya Gokhale <gokhale2@...l.gov>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Martin Cracauer <cracauer@...s.org>, Shaohua Li <shli@...com>,
        Marty McFadden <mcfadden8@...l.gov>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Denis Plotnikov <dplotnikov@...tuozzo.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Mel Gorman <mgorman@...e.de>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>
Subject: Re: [PATCH v2 19/26] userfaultfd: introduce helper vma_find_uffd

On Tue, Feb 12, 2019 at 10:56:25AM +0800, Peter Xu wrote:
> We've have multiple (and more coming) places that would like to find a
> userfault enabled VMA from a mm struct that covers a specific memory
> range.  This patch introduce the helper for it, meanwhile apply it to
> the code.
> 
> Suggested-by: Mike Rapoport <rppt@...ux.vnet.ibm.com>
> Signed-off-by: Peter Xu <peterx@...hat.com>

Reviewed-by: Jérôme Glisse <jglisse@...hat.com>

> ---
>  mm/userfaultfd.c | 54 +++++++++++++++++++++++++++---------------------
>  1 file changed, 30 insertions(+), 24 deletions(-)
> 
> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
> index 80bcd642911d..fefa81c301b7 100644
> --- a/mm/userfaultfd.c
> +++ b/mm/userfaultfd.c
> @@ -20,6 +20,34 @@
>  #include <asm/tlbflush.h>
>  #include "internal.h"
>  
> +/*
> + * Find a valid userfault enabled VMA region that covers the whole
> + * address range, or NULL on failure.  Must be called with mmap_sem
> + * held.
> + */
> +static struct vm_area_struct *vma_find_uffd(struct mm_struct *mm,
> +					    unsigned long start,
> +					    unsigned long len)
> +{
> +	struct vm_area_struct *vma = find_vma(mm, start);
> +
> +	if (!vma)
> +		return NULL;
> +
> +	/*
> +	 * Check the vma is registered in uffd, this is required to
> +	 * enforce the VM_MAYWRITE check done at uffd registration
> +	 * time.
> +	 */
> +	if (!vma->vm_userfaultfd_ctx.ctx)
> +		return NULL;
> +
> +	if (start < vma->vm_start || start + len > vma->vm_end)
> +		return NULL;
> +
> +	return vma;
> +}
> +
>  static int mcopy_atomic_pte(struct mm_struct *dst_mm,
>  			    pmd_t *dst_pmd,
>  			    struct vm_area_struct *dst_vma,
> @@ -228,20 +256,9 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
>  	 */
>  	if (!dst_vma) {
>  		err = -ENOENT;
> -		dst_vma = find_vma(dst_mm, dst_start);
> +		dst_vma = vma_find_uffd(dst_mm, dst_start, len);
>  		if (!dst_vma || !is_vm_hugetlb_page(dst_vma))
>  			goto out_unlock;
> -		/*
> -		 * Check the vma is registered in uffd, this is
> -		 * required to enforce the VM_MAYWRITE check done at
> -		 * uffd registration time.
> -		 */
> -		if (!dst_vma->vm_userfaultfd_ctx.ctx)
> -			goto out_unlock;
> -
> -		if (dst_start < dst_vma->vm_start ||
> -		    dst_start + len > dst_vma->vm_end)
> -			goto out_unlock;
>  
>  		err = -EINVAL;
>  		if (vma_hpagesize != vma_kernel_pagesize(dst_vma))
> @@ -488,20 +505,9 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
>  	 * both valid and fully within a single existing vma.
>  	 */
>  	err = -ENOENT;
> -	dst_vma = find_vma(dst_mm, dst_start);
> +	dst_vma = vma_find_uffd(dst_mm, dst_start, len);
>  	if (!dst_vma)
>  		goto out_unlock;
> -	/*
> -	 * Check the vma is registered in uffd, this is required to
> -	 * enforce the VM_MAYWRITE check done at uffd registration
> -	 * time.
> -	 */
> -	if (!dst_vma->vm_userfaultfd_ctx.ctx)
> -		goto out_unlock;
> -
> -	if (dst_start < dst_vma->vm_start ||
> -	    dst_start + len > dst_vma->vm_end)
> -		goto out_unlock;
>  
>  	err = -EINVAL;
>  	/*
> -- 
> 2.17.1
>