linux-kernel - [PATCH RFC 11/17] userfaultfd: mfill

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Message-ID: <20260127192936.1250096-12-rppt@kernel.org>
Date: Tue, 27 Jan 2026 21:29:30 +0200
From: Mike Rapoport <rppt@...nel.org>
To: linux-mm@...ck.org
Cc: Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Axel Rasmussen <axelrasmussen@...gle.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	David Hildenbrand <david@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	James Houghton <jthoughton@...gle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Michal Hocko <mhocko@...e.com>,
	Mike Rapoport <rppt@...nel.org>,
	Muchun Song <muchun.song@...ux.dev>,
	Nikita Kalyazin <kalyazin@...zon.com>,
	Oscar Salvador <osalvador@...e.de>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Peter Xu <peterx@...hat.com>,
	Sean Christopherson <seanjc@...gle.com>,
	Shuah Khan <shuah@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Subject: [PATCH RFC 11/17] userfaultfd: mfill_atomic() remove retry logic

From: "Mike Rapoport (Microsoft)" <rppt@...nel.org>

Since __mfill_atomic_pte() handles the retry for both anonymous and
shmem, there is no need to retry copying the date from the userspace in
the loop in mfill_atomic().

Drop the retry logic from mfill_atomic().

Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
---
 mm/userfaultfd.c | 24 ------------------------
 1 file changed, 24 deletions(-)

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 54aa195237ba..1bd7631463c6 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -29,7 +29,6 @@ struct mfill_state {
 	struct vm_area_struct *vma;
 	unsigned long src_addr;
 	unsigned long dst_addr;
-	struct folio *folio;
 	pmd_t *pmd;
 };
 
@@ -889,7 +888,6 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx,
 	VM_WARN_ON_ONCE(src_start + len <= src_start);
 	VM_WARN_ON_ONCE(dst_start + len <= dst_start);
 
-retry:
 	err = mfill_get_vma(&state);
 	if (err)
 		goto out;
@@ -916,26 +914,6 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx,
 		err = mfill_atomic_pte(&state);
 		cond_resched();
 
-		if (unlikely(err == -ENOENT)) {
-			void *kaddr;
-
-			mfill_put_vma(&state);
-			VM_WARN_ON_ONCE(!state.folio);
-
-			kaddr = kmap_local_folio(state.folio, 0);
-			err = copy_from_user(kaddr,
-					     (const void __user *)state.src_addr,
-					     PAGE_SIZE);
-			kunmap_local(kaddr);
-			if (unlikely(err)) {
-				err = -EFAULT;
-				goto out;
-			}
-			flush_dcache_folio(state.folio);
-			goto retry;
-		} else
-			VM_WARN_ON_ONCE(state.folio);
-
 		if (!err) {
 			state.dst_addr += PAGE_SIZE;
 			state.src_addr += PAGE_SIZE;
@@ -951,8 +929,6 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx,
 	if (state.vma)
 		mfill_put_vma(&state);
 out:
-	if (state.folio)
-		folio_put(state.folio);
 	VM_WARN_ON_ONCE(copied < 0);
 	VM_WARN_ON_ONCE(err > 0);
 	VM_WARN_ON_ONCE(!copied && !err);
-- 
2.51.0