From nobody Sun Feb 8 14:13:00 2026 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 81D2D36E49A; Tue, 27 Jan 2026 19:31:09 +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=1769542269; cv=none; b=LxTXy+0XqLmMMvTNzOMjgqECiWxHdZWQ+uiU4VRL/yOJrjR1lqSTp5SqULl/JNThPp9O5Ef+eM///Bhp2fZi8SmyLRAZOEZ2nkGtDcVvMiI29vUi2rX414nf5vWO+nVHZjt/iTK9TlU8n/ZKm4vWBPxU3zskRjse8+AMVo2YO/M= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769542269; c=relaxed/simple; bh=+RlyxhG8wPwYaWoZfV3wHqPdgp7OwXA/s55MoAiNhJU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=syT8WJwSamsFt+MgIVNNL2Ogu/2Z1/ZjMTV8qz0tx44qkqehcvzku7NuG2d54pQ37oaLVlESc94T0Ia3PVyVCxlJytNSWVajdpBQ2iFnK+omsv2GCwhSetvrORqx5RQg5Ek6q+X0zo5gA/18aYSCyxMuuHoFiwGYtgyCxS1gHok= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hxCun7NY; 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="hxCun7NY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 72991C116C6; Tue, 27 Jan 2026 19:31:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1769542269; bh=+RlyxhG8wPwYaWoZfV3wHqPdgp7OwXA/s55MoAiNhJU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=hxCun7NYeayN6IkquZNPDK6UUnd1cAbljA2eL0BVX9w58wypp6/mCfqTEe8bHxP5a HG4OouTbgYoMhHWfngWLGr5c2/z/XbLR5ETtxzfmFLGLns51cPfDLBrvvSUx18cp4e ndfN0qt9j/sfkyHEqyjwx8YVt5nPQE3T389NiQ0VWC92VxIiaSBx8/e+63FoGVxIWZ 4Zcs+7dyUpegnBUsSn5MbvHtNdkIrtfxEYCtVqLblH1y7e4cMmySJc/k11QIs8g/Uh WmM/cmFVYJd2vqUFcJ9yZ5uiwJ7k1/o/TOfpz73DmNLM4l61/9gwO/XPQZdiZ3f8kT v+fkzz1g90MJQ== 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 , Muchun Song , Nikita Kalyazin , Oscar Salvador , 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 Subject: [PATCH RFC 13/17] mm: introduce VM_FAULT_UFFD_MISSING fault reason Date: Tue, 27 Jan 2026 21:29:32 +0200 Message-ID: <20260127192936.1250096-14-rppt@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260127192936.1250096-1-rppt@kernel.org> References: <20260127192936.1250096-1-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: Nikita Kalyazin When a VMA is registered with userfaulfd in missing mode, its ->fault() method should check if a folio exists in the page cache and if no ->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_MISSING 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_MISSING there instead. For configurations that don't enable CONFIG_USERFAULTFD, VM_FAULT_UFFD_MISSING is set to 0. Signed-off-by: Nikita Kalyazin Signed-off-by: Mike Rapoport (Microsoft) --- include/linux/mm_types.h | 7 ++++++- mm/memory.c | 5 ++++- mm/shmem.c | 2 +- 3 files changed, 11 insertions(+), 3 deletions(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index b25ac322bfbf..a061c43e835b 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -1557,6 +1557,8 @@ typedef __bitwise unsigned int vm_fault_t; * @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_UFFD_MISSING: ->fault did not modify page tables and needs + * handle_userfault(VM_UFFD_MISSING) to complete * @VM_FAULT_HINDEX_MASK: mask HINDEX value * */ @@ -1576,8 +1578,10 @@ enum vm_fault_reason { VM_FAULT_COMPLETED =3D (__force vm_fault_t)0x004000, #ifdef CONFIG_USERFAULTFD VM_FAULT_UFFD_MINOR =3D (__force vm_fault_t)0x008000, + VM_FAULT_UFFD_MISSING =3D (__force vm_fault_t)0x010000, #else VM_FAULT_UFFD_MINOR =3D (__force vm_fault_t)0x000000, + VM_FAULT_UFFD_MISSING =3D (__force vm_fault_t)0x000000, #endif VM_FAULT_HINDEX_MASK =3D (__force vm_fault_t)0x0f0000, }; @@ -1604,7 +1608,8 @@ enum vm_fault_reason { { VM_FAULT_DONE_COW, "DONE_COW" }, \ { VM_FAULT_NEEDDSYNC, "NEEDDSYNC" }, \ { VM_FAULT_COMPLETED, "COMPLETED" }, \ - { VM_FAULT_UFFD_MINOR, "UFFD_MINOR" } + { VM_FAULT_UFFD_MINOR, "UFFD_MINOR" }, \ + { VM_FAULT_UFFD_MISSING, "UFFD_MISSING" } =20 struct vm_special_mapping { const char *name; /* The name, e.g. "[vdso]". */ diff --git a/mm/memory.c b/mm/memory.c index fcb3e0c3113e..f72e69a43b68 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -5319,9 +5319,12 @@ static vm_fault_t __do_fault(struct vm_fault *vmf) =20 ret =3D vma->vm_ops->fault(vmf); if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY | - VM_FAULT_DONE_COW | VM_FAULT_UFFD_MINOR))) { + VM_FAULT_DONE_COW | VM_FAULT_UFFD_MINOR | + VM_FAULT_UFFD_MISSING))) { if (ret & VM_FAULT_UFFD_MINOR) return handle_userfault(vmf, VM_UFFD_MINOR); + if (ret & VM_FAULT_UFFD_MISSING) + return handle_userfault(vmf, VM_UFFD_MISSING); return ret; } =20 diff --git a/mm/shmem.c b/mm/shmem.c index 6aa905147c0c..1bc544cab2a8 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2530,7 +2530,7 @@ static int shmem_get_folio_gfp(struct inode *inode, p= goff_t index, */ =20 if (vma && userfaultfd_missing(vma)) { - *fault_type =3D handle_userfault(vmf, VM_UFFD_MISSING); + *fault_type =3D VM_FAULT_UFFD_MISSING; return 0; } =20 --=20 2.51.0