linux-kernel - [PATCH v1 2/9] mm/memory: handle !page case in zap_present

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Message-ID: <20240129143221.263763-3-david@redhat.com>
Date: Mon, 29 Jan 2024 15:32:14 +0100
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
	David Hildenbrand <david@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matthew Wilcox <willy@...radead.org>,
	Ryan Roberts <ryan.roberts@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
	Nick Piggin <npiggin@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	"Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>,
	Arnd Bergmann <arnd@...db.de>,
	linux-arch@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org,
	linux-s390@...r.kernel.org
Subject: [PATCH v1 2/9] mm/memory: handle !page case in zap_present_pte() separately

We don't need uptodate accessed/dirty bits, so in theory we could
replace ptep_get_and_clear_full() by an optimized ptep_clear_full()
function. Let's rely on the provided pte.

Further, there is no scenario where we would have to insert uffd-wp
markers when zapping something that is not a normal page (i.e., zeropage).
Add a sanity check to make sure this remains true.

should_zap_folio() no longer has to handle NULL pointers. This change
replaces 2/3 "!page/!folio" checks by a single "!page" one.

Signed-off-by: David Hildenbrand <david@...hat.com>
---
 mm/memory.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 50a6c79c78fc..69502cdc0a7d 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1497,10 +1497,6 @@ static inline bool should_zap_folio(struct zap_details *details,
 	if (should_zap_cows(details))
 		return true;
 
-	/* E.g. the caller passes NULL for the case of a zero folio */
-	if (!folio)
-		return true;
-
 	/* Otherwise we should only zap non-anon folios */
 	return !folio_test_anon(folio);
 }
@@ -1543,19 +1539,23 @@ static inline void zap_present_pte(struct mmu_gather *tlb,
 	struct page *page;
 
 	page = vm_normal_page(vma, addr, ptent);
-	if (page)
-		folio = page_folio(page);
+	if (!page) {
+		/* We don't need up-to-date accessed/dirty bits. */
+		ptep_get_and_clear_full(mm, addr, pte, tlb->fullmm);
+		arch_check_zapped_pte(vma, ptent);
+		tlb_remove_tlb_entry(tlb, pte, addr);
+		VM_WARN_ON_ONCE(userfaultfd_wp(vma));
+		ksm_might_unmap_zero_page(mm, ptent);
+		return;
+	}
 
+	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 (unlikely(!page)) {
-		ksm_might_unmap_zero_page(mm, ptent);
-		return;
-	}
 
 	if (!folio_test_anon(folio)) {
 		if (pte_dirty(ptent)) {
-- 
2.43.0