drivers/virt/fsl_hypervisor.c: use get_user_pages_unlocked()

Moving from get_user_pages() to get_user_pages_unlocked() simplifies the
code and takes advantage of VM_FAULT_RETRY functionality when faulting
in pages.

Link: http://lkml.kernel.org/r/20161101194332.23961-1-lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Kumar Gala <galak@kernel.crashing.org>
Cc: Mihai Caraman <mihai.caraman@freescale.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/virt/fsl_hypervisor.c

@@ -243,11 +243,8 @@ static long ioctl_memcpy(struct fsl_hv_ioctl_memcpy __user *p)
 	sg_list = PTR_ALIGN(sg_list_unaligned, sizeof(struct fh_sg_list));
 
 	/* Get the physical addresses of the source buffer */
-	down_read(&current->mm->mmap_sem);
-	num_pinned = get_user_pages(param.local_vaddr - lb_offset,
-		num_pages, (param.source == -1) ? 0 : FOLL_WRITE,
-		pages, NULL);
-	up_read(&current->mm->mmap_sem);
+	num_pinned = get_user_pages_unlocked(param.local_vaddr - lb_offset,
+		num_pages, pages, (param.source == -1) ? 0 : FOLL_WRITE);
 
 	if (num_pinned != num_pages) {
 		/* get_user_pages() failed */