xen: use vma_lookup() in privcmd_ioctl_mmap()

vma_lookup() walks the VMA tree for a specific value, find_vma() will
search the tree after walking to a specific value.  It is more efficient
to only walk to the requested value since privcmd_ioctl_mmap() will exit
the loop if vm_start != msg->va.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Liam R. Howlett <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Tested-by: Yu Zhao <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: David Howells <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: "Matthew Wilcox (Oracle)" <[email protected]>
Cc: SeongJae Park <[email protected]>
Cc: Sven Schnelle <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: howlett

drivers/xen/privcmd.c

@@ -282,7 +282,7 @@ static long privcmd_ioctl_mmap(struct file *file, void __user *udata)
 						     struct page, lru);
 		struct privcmd_mmap_entry *msg = page_address(page);
 
-		vma = find_vma(mm, msg->va);
+		vma = vma_lookup(mm, msg->va);
 		rc = -EINVAL;
 
 		if (!vma || (msg->va != vma->vm_start) || vma->vm_private_data)