[Devel] [PATCH RHEL8 COMMIT] userfaultfd: wrap the common dst_vma check into an inlined function

[Konstantin Khorenko]

The commit is pushed to "branch-rh8-4.18.0-80.1.2.vz8.3.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh8-4.18.0-80.1.2.vz8.3.6
------>
commit c5f8ba9ff036598c6206529dbc480073c1e15445
Author: Wei Yang <richardw.yang at linux.intel.com>
Date:   Mon Apr 20 10:34:05 2020 +0300

    userfaultfd: wrap the common dst_vma check into an inlined function
    
    When doing UFFDIO_COPY, it is necessary to find the correct destination
    vma and make sure fault range is in it.
    
    Since there are two places need to do the same task, just wrap those
    common check into an inlined function.
    
    Link: http://lkml.kernel.org/r/20190927070032.2129-3-richardw.yang@linux.intel.com
    Signed-off-by: Wei Yang <richardw.yang at linux.intel.com>
    Reviewed-by: Mike Kravetz <mike.kravetz at oracle.com>
    Cc: Andrea Arcangeli <aarcange at redhat.com>
    Cc: Hugh Dickins <hughd at google.com>
    Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
    
    https://jira.sw.ru/browse/PSBM-102938
    (cherry picked from commit 643aa36eadebdcdcaeecf538f0549a619ad78ea0)
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 mm/userfaultfd.c | 56 ++++++++++++++++++++++++++++++++------------------------
 1 file changed, 32 insertions(+), 24 deletions(-)

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 458acda96f20..8d26d35f1203 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -20,6 +20,36 @@
 #include <asm/tlbflush.h>
 #include "internal.h"
 
+static __always_inline
+struct vm_area_struct *find_dst_vma(struct mm_struct *dst_mm,
+				    unsigned long dst_start,
+				    unsigned long len)
+{
+	/*
+	 * Make sure that the dst range is both valid and fully within a
+	 * single existing vma.
+	 */
+	struct vm_area_struct *dst_vma;
+
+	dst_vma = find_vma(dst_mm, dst_start);
+	if (!dst_vma)
+		return NULL;
+
+	if (dst_start < dst_vma->vm_start ||
+	    dst_start + len > dst_vma->vm_end)
+		return NULL;
+
+	/*
+	 * 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)
+		return NULL;
+
+	return dst_vma;
+}
+
 static int mcopy_atomic_pte(struct mm_struct *dst_mm,
 			    pmd_t *dst_pmd,
 			    struct vm_area_struct *dst_vma,
@@ -223,20 +253,9 @@ 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 = find_dst_vma(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))
@@ -478,20 +497,9 @@ 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 = find_dst_vma(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;
 	/*