mm/memory: further separate anon and pagecache folio handling in zap_present_pte()

We don't need up-to-date accessed-dirty information for anon folios and
can simply work with the ptent we already have.  Also, we know the RSS
counter we want to update.

We can safely move arch_check_zapped_pte() + tlb_remove_tlb_entry() +
zap_install_uffd_wp_if_needed() after updating the folio and RSS.

While at it, only call zap_install_uffd_wp_if_needed() if there is even
any chance that pte_install_uffd_wp_if_needed() would do *something*. 
That is, just don't bother if uffd-wp does not apply.

Link: https://lkml.kernel.org/r/20240214204435.167852-4-david@redhat.comSigned-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yin Fengwei <fengwei.yin@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/memory.c

@@ -1554,12 +1554,9 @@ static inline void zap_present_pte(struct mmu_gather *tlb,
 	folio = page_folio(page);
 	if (unlikely(!should_zap_folio(details, folio)))
 		return;
-	ptent = ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm);
-	arch_check_zapped_pte(vma, ptent);
-	tlb_remove_tlb_entry(tlb, pte, addr);
-	zap_install_uffd_wp_if_needed(vma, addr, pte, details, ptent);
 
 	if (!folio_test_anon(folio)) {
+		ptent = ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm);
 		if (pte_dirty(ptent)) {
 			folio_mark_dirty(folio);
 			if (tlb_delay_rmap(tlb)) {
@@ -1569,8 +1566,17 @@ static inline void zap_present_pte(struct mmu_gather *tlb,
 		}
 		if (pte_young(ptent) && likely(vma_has_recency(vma)))
 			folio_mark_accessed(folio);
-	}
 		rss[mm_counter(folio)]--;
+	} else {
+		/* We don't need up-to-date accessed/dirty bits. */
+		ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm);
+		rss[MM_ANONPAGES]--;
+	}
+	arch_check_zapped_pte(vma, ptent);
+	tlb_remove_tlb_entry(tlb, pte, addr);
+	if (unlikely(userfaultfd_pte_wp(vma, ptent)))
+		zap_install_uffd_wp_if_needed(vma, addr, pte, details, ptent);
+
 	if (!delay_rmap) {
 		folio_remove_rmap_pte(folio, page, vma);
 		if (unlikely(page_mapcount(page) < 0))