From: David Hildenbrand (Arm) <david@kernel.org>
Date: Fri, 27 Feb 2026 20:08:40 +0000 (+0100)
Subject: mm/memory: convert details->even_cows into details->skip_cows
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=a97bc13d15f472c7f8ede1b38660fb55b6dab68d;p=thirdparty%2Flinux.git

mm/memory: convert details->even_cows into details->skip_cows

The current semantics are confusing: simply because someone specifies an
empty zap_detail struct suddenly makes should_zap_cows() behave
differently.  The default should be to also zap CoW'ed anonymous pages.

Really only unmap_mapping_pages() and friends want to skip zapping of
these anon folios.

So let's invert the meaning; turn the confusing "reclaim_pt" check that
overrides other properties in should_zap_cows() into a safety check.

Note that the only caller that sets reclaim_pt=true is
madvise_dontneed_single_vma(), which wants to zap any pages.

Link: https://lkml.kernel.org/r/20260227200848.114019-10-david@kernel.org
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Arve <arve@android.com>
Cc: "Borislav Petkov (AMD)" <bp@alien8.de>
Cc: Carlos Llamas <cmllamas@google.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Daniel Borkman <daniel@iogearbox.net>
Cc: Dave Airlie <airlied@gmail.com>
Cc: David Ahern <dsahern@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Dimitri Sivanich <dimitri.sivanich@hpe.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jakub Kacinski <kuba@kernel.org>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Jann Horn <jannh@google.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Jarkko Sakkinen <jarkko@kernel.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Namhyung kim <namhyung@kernel.org>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Todd Kjos <tkjos@android.com>
Cc: Tvrtko Ursulin <tursulin@ursulin.net>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 771d021b79483..cb4f5fbccaf07 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2767,7 +2767,7 @@ extern void pagefault_out_of_memory(void);
  */
 struct zap_details {
 	struct folio *single_folio;	/* Locked folio to be unmapped */
-	bool even_cows;			/* Zap COWed private pages too? */
+	bool skip_cows;			/* Do not zap COWed private pages */
 	bool reclaim_pt;		/* Need reclaim page tables? */
 	zap_flags_t zap_flags;		/* Extra flags for zapping */
 };
diff --git a/mm/madvise.c b/mm/madvise.c
index e4a2728593a84..e862286828423 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -853,7 +853,6 @@ static long madvise_dontneed_single_vma(struct madvise_behavior *madv_behavior)
 	struct madvise_behavior_range *range = &madv_behavior->range;
 	struct zap_details details = {
 		.reclaim_pt = true,
-		.even_cows = true,
 	};
 
 	zap_page_range_single_batched(
diff --git a/mm/memory.c b/mm/memory.c
index 7e5d52534ee90..c66b7b8b47eb8 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1554,11 +1554,13 @@ copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
 static inline bool should_zap_cows(struct zap_details *details)
 {
 	/* By default, zap all pages */
-	if (!details || details->reclaim_pt)
+	if (!details)
 		return true;
 
+	VM_WARN_ON_ONCE(details->skip_cows && details->reclaim_pt);
+
 	/* Or, we zap COWed pages only if the caller wants to */
-	return details->even_cows;
+	return !details->skip_cows;
 }
 
 /* Decides whether we should zap this folio with the folio pointer specified */
@@ -2149,8 +2151,6 @@ void unmap_vmas(struct mmu_gather *tlb, struct unmap_desc *unmap)
 	struct mmu_notifier_range range;
 	struct zap_details details = {
 		.zap_flags = ZAP_FLAG_DROP_MARKER | ZAP_FLAG_UNMAP,
-		/* Careful - we need to zap private pages too! */
-		.even_cows = true,
 	};
 
 	vma = unmap->first;
@@ -4282,7 +4282,7 @@ void unmap_mapping_folio(struct folio *folio)
 	first_index = folio->index;
 	last_index = folio_next_index(folio) - 1;
 
-	details.even_cows = false;
+	details.skip_cows = true;
 	details.single_folio = folio;
 	details.zap_flags = ZAP_FLAG_DROP_MARKER;
 
@@ -4312,7 +4312,7 @@ void unmap_mapping_pages(struct address_space *mapping, pgoff_t start,
 	pgoff_t	first_index = start;
 	pgoff_t	last_index = start + nr - 1;
 
-	details.even_cows = even_cows;
+	details.skip_cows = !even_cows;
 	if (last_index < first_index)
 		last_index = ULONG_MAX;