Re: [PATCH v2 19/26] userfaultfd: introduce helper vma_find_uffd

From: Mike Rapoport <rppt@linux.ibm.com>
To: Peter Xu <peterx@redhat.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	David Hildenbrand <david@redhat.com>,
	Hugh Dickins <hughd@google.com>, Maya Gokhale <gokhale2@llnl.gov>,
	Jerome Glisse <jglisse@redhat.com>,
	Pavel Emelyanov <xemul@virtuozzo.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Martin Cracauer <cracauer@cons.org>, Shaohua Li <shli@fb.com>,
	Marty McFadden <mcfadden8@llnl.gov>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Denis Plotnikov <dplotnikov@virtuozzo.com>,
	Mike Rapoport <rppt@linux.vnet.ibm.com>,
	Mel Gorman <mgorman@suse.de>,
	"Kirill A . Shutemov" <kirill@shutemov.name>,
	"Dr . David Alan Gilbert" <dgilbert@redhat.com>
Subject: Re: [PATCH v2 19/26] userfaultfd: introduce helper vma_find_uffd
Date: Mon, 25 Feb 2019 22:48:15 +0200	[thread overview]
Message-ID: <20190225204815.GB10454@rapoport-lnx> (raw)
In-Reply-To: <20190212025632.28946-20-peterx@redhat.com>

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@linux.vnet.ibm.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>

Reviewed-by: Mike Rapoport <rppt@linux.ibm.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
> 

-- 
Sincerely yours,
Mike.