mm: set pte writable while pte_soft_dirty() is true in do_swap_page()

This patch leverages the new pte_needs_soft_dirty_wp() helper to optimize
a scenario where softdirty is enabled, but the softdirty flag has already
been set in do_swap_page().  In this situation, we can use pte_mkwrite
instead of applying write-protection since we don't depend on write
faults.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Barry Song <[email protected]>
Suggested-by: David Hildenbrand <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Cc: Chris Li <[email protected]>
Cc: Kairui Song <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Barry Song

mm/memory.c

@@ -4324,7 +4324,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	if (!folio_test_ksm(folio) &&
 	    (exclusive || folio_ref_count(folio) == 1)) {
 		if ((vma->vm_flags & VM_WRITE) && !userfaultfd_pte_wp(vma, pte) &&
-		    !vma_soft_dirty_enabled(vma)) {
+		    !pte_needs_soft_dirty_wp(vma, pte)) {
 			pte = pte_mkwrite(pte, vma);
 			if (vmf->flags & FAULT_FLAG_WRITE) {
 				pte = pte_mkdirty(pte);