mm: move FAULT_FLAG_VMA_LOCK check down in handle_pte_fault()

Call do_pte_missing() under the VMA lock ...  then immediately retry in
do_fault().

Link: https://lkml.kernel.org/r/20230724185410.1124082-7-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Cc: Arjun Roy <arjunroy@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Punit Agrawal <punit.agrawal@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/memory.c

@@ -4647,6 +4647,11 @@ static vm_fault_t do_fault(struct vm_fault *vmf)
 	struct mm_struct *vm_mm = vma->vm_mm;
 	vm_fault_t ret;
 
+	if (vmf->flags & FAULT_FLAG_VMA_LOCK){
+		vma_end_read(vma);
+		return VM_FAULT_RETRY;
+	}
+
 	/*
 	 * The VMA was not fully populated on mmap() or missing VM_DONTEXPAND
 	 */
@@ -4932,11 +4937,6 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
 {
 	pte_t entry;
 
-	if ((vmf->flags & FAULT_FLAG_VMA_LOCK) && !vma_is_anonymous(vmf->vma)) {
-		vma_end_read(vmf->vma);
-		return VM_FAULT_RETRY;
-	}
-
 	if (unlikely(pmd_none(*vmf->pmd))) {
 		/*
 		 * Leave __pte_alloc() until later: because vm_ops->fault may
@@ -4969,6 +4969,12 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
 	if (!vmf->pte)
 		return do_pte_missing(vmf);
 
+	if ((vmf->flags & FAULT_FLAG_VMA_LOCK) && !vma_is_anonymous(vmf->vma)) {
+		pte_unmap(vmf->pte);
+		vma_end_read(vmf->vma);
+		return VM_FAULT_RETRY;
+	}
+
 	if (!pte_present(vmf->orig_pte))
 		return do_swap_page(vmf);