From nobody Tue Dec 2 01:24:49 2025 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 38E002C15A5; Sun, 23 Nov 2025 10:27:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763893654; cv=none; b=tt92Ut4pDiTTytPc945sDtEs1i1su6bSeWGZii9yrRhX9ViN6YrGMLcnTT0AcPPvuMDlwoliRtv6b3pOXFVogx4rI0OgtufrV7G9Qm8l+hS+OxcoUA3syEHkTc77KLSVMN/oQ6I15LxNQnvJSG8TKPb/pvNHV57kYv03ieC0gJc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763893654; c=relaxed/simple; bh=TGp6vvbLTdhwYnCuBgb7XJ6N0yTp/sgeTzqO6gH5CkQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=OUl7oikWjC6WmU8GXbmyQXHK5x8b0J7rK9QyDeObA/ybFFukI43ADyoJhq18FcNxD+NMhdskRAj7p+U+A6j5j8IMiRV77RBcVSyKOVxoF6C/71WWhnBLedeadovaaLGFbFWzr8/uQhSSlmJOvPbMgS60Q9D+YxdJd61z/lslVsI= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OBrZFSOb; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="OBrZFSOb" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 74B67C113D0; Sun, 23 Nov 2025 10:27:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763893653; bh=TGp6vvbLTdhwYnCuBgb7XJ6N0yTp/sgeTzqO6gH5CkQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=OBrZFSObtudrp9MGuTQx1JbCUW5/SlKmBilfqqt7cVta7+2osmrx6ZyWfiBxv7L+S mv/oSxzGa9Pj5oyj6UeFbBqXqa/DnMTvwBT/sA1csuz0mHlB89qW61bP7HwGxsGmg9 F0BrGRGIL6+ooQN6dT1CUYLo5WiQmeqG2J4vOJ4YlPKml3KDHUbncQtw2KIOgD+gK3 n33A0tSjubrO9zwq2egBfRT0z9/XLeBTBTRDwuZmtjoAnb2WM7jM2hA1KBwKkJzB8+ tuj7yk1fsO69UQ/8E3JifeiIs6M9V5DAx1SDwyL5RS6CqOcD86pyfDzyQs5eYwe59O xR3EW4IXNx/xw== From: Mike Rapoport To: linux-mm@kvack.org Cc: Andrea Arcangeli , Andrew Morton , Axel Rasmussen , Baolin Wang , David Hildenbrand , Hugh Dickins , James Houghton , "Liam R. Howlett" , Lorenzo Stoakes , Michal Hocko , Mike Rapoport , Nikita Kalyazin , Paolo Bonzini , Peter Xu , Sean Christopherson , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, "David Hildenbrand (Red Hat)" Subject: [PATCH 3/5] mm: introduce VM_FAULT_UFFD_MINOR fault reason Date: Sun, 23 Nov 2025 12:27:05 +0200 Message-ID: <20251123102707.559422-4-rppt@kernel.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20251123102707.559422-1-rppt@kernel.org> References: <20251123102707.559422-1-rppt@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: "Mike Rapoport (Microsoft)" When a VMA is registered with userfaulfd in minor mode, its ->fault() method should check if a folio exists in the page cache and if yes ->fault() should call handle_userfault(VM_UFFD_MISSING). Instead of calling handle_userfault() directly from a specific ->fault() implementation introduce new fault reason VM_FAULT_UFFD_MINOR that will notify the core page fault handler that it should call handle_userfaultfd(VM_UFFD_MISSING) to complete a page fault. Replace a call to handle_userfault(VM_UFFD_MISSING) in shmem and use the new VM_FAULT_UFFD_MINOR there instead. Suggested-by: David Hildenbrand (Red Hat) Signed-off-by: Mike Rapoport (Microsoft) --- include/linux/mm_types.h | 3 +++ mm/memory.c | 2 ++ mm/shmem.c | 2 +- 3 files changed, 6 insertions(+), 1 deletion(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 90e5790c318f..eb135369940f 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -1523,6 +1523,8 @@ typedef __bitwise unsigned int vm_fault_t; * fsync() to complete (for synchronous page faults * in DAX) * @VM_FAULT_COMPLETED: ->fault completed, meanwhile mmap lock released + * @VM_FAULT_UFFD_MINOR: ->fault did not modify page tables and needs + * handle_userfault(VM_UFFD_MINOR) to complete * @VM_FAULT_HINDEX_MASK: mask HINDEX value * */ @@ -1540,6 +1542,7 @@ enum vm_fault_reason { VM_FAULT_DONE_COW =3D (__force vm_fault_t)0x001000, VM_FAULT_NEEDDSYNC =3D (__force vm_fault_t)0x002000, VM_FAULT_COMPLETED =3D (__force vm_fault_t)0x004000, + VM_FAULT_UFFD_MINOR =3D (__force vm_fault_t)0x008000, VM_FAULT_HINDEX_MASK =3D (__force vm_fault_t)0x0f0000, }; =20 diff --git a/mm/memory.c b/mm/memory.c index b59ae7ce42eb..94acbac8cefb 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -5279,6 +5279,8 @@ static vm_fault_t __do_fault(struct vm_fault *vmf) } =20 ret =3D vma->vm_ops->fault(vmf); + if (unlikely(ret & VM_FAULT_UFFD_MINOR)) + return handle_userfault(vmf, VM_UFFD_MINOR); if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY | VM_FAULT_DONE_COW))) return ret; diff --git a/mm/shmem.c b/mm/shmem.c index aaa21bb60f51..6dcb73b52bcc 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2461,7 +2461,7 @@ static int shmem_get_folio_gfp(struct inode *inode, p= goff_t index, if (folio && vma && userfaultfd_minor(vma)) { if (!xa_is_value(folio)) folio_put(folio); - *fault_type =3D handle_userfault(vmf, VM_UFFD_MINOR); + *fault_type =3D VM_FAULT_UFFD_MINOR; return 0; } =20 --=20 2.50.1