From nobody Tue Dec 2 00:25:26 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 72240332900; Tue, 25 Nov 2025 18:39:07 +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=1764095947; cv=none; b=VKeoI9RXXBUK42x5MlFL+Aud4AmwxzBBM7t5k/EoLXM9FYCwYC90EosUGgKnq8/2Al8Px26y17DfQaGcS+ZlTxnbvQqAAetE1XHqaimh0kFbke00ZKdZSdAHFLkbfRZ7Kn9jWpKha1eBtZ0oA+9nqiE04QH09IyhRYUDm4SH6Lo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764095947; c=relaxed/simple; bh=OMs5feUckVCg3jntuqU22gZ/ufy0V9GaFPtJ4+nCsbQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=QPx1PXRQveFyNznk64KEMzfnD+LaVqjvVn4Lz2+Uh1i1NxjfU6e5eFgThTuYEGCBgdsjjiLihhtt7whCFbiTO5zCyMWEPpXn3f+OGRDisZ/OeK9fy/rJGHmQries7JLWC5zDyFtwiBfQENj6AkqM2vPHoAxL82EQJ0ppSSISvck= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=k+rjAQwX; 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="k+rjAQwX" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E139DC19422; Tue, 25 Nov 2025 18:39:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1764095947; bh=OMs5feUckVCg3jntuqU22gZ/ufy0V9GaFPtJ4+nCsbQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=k+rjAQwX+9oyD23In9ooJMuiZlgSjVe7F3a6uIEgz1GZ4RWJmAVwRq1A3GX0F11g8 WpbUvXAxGYRUz92F99Q31i/6oM4ExJUMNRmsybLKQme98QngVmtlLHeXJ8Td9Av+WA lR1AWyV+or429S5CqW7LTi+L5VVrghZlv+Hv9eOyXNrWjN4+Jv6fllrLCy+6dK4hXc J7LSRDv/TDGREvUaiVhFkFF6O5aSi9KW8pDWeVgykB4wU5N6LDOWfpObOmg2NG3s+h 4HxcYX0LT2C8ThnZbwWmQvS81JGFvtbFBrzs9A8Or9xTaLwr1yR1MLPG9UB8ZBlWMc qhMk5fLNWc7mw== 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 v2 3/5] mm: introduce VM_FAULT_UFFD_MINOR fault reason Date: Tue, 25 Nov 2025 20:38:38 +0200 Message-ID: <20251125183840.2368510-4-rppt@kernel.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20251125183840.2368510-1-rppt@kernel.org> References: <20251125183840.2368510-1-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. For configurations that don't enable CONFIG_USERFAULTFD, VM_FAULT_UFFD_MINOR is set to 0. Suggested-by: David Hildenbrand (Red Hat) Signed-off-by: Mike Rapoport (Microsoft) --- include/linux/mm_types.h | 10 +++++++++- mm/memory.c | 2 ++ mm/shmem.c | 2 +- 3 files changed, 12 insertions(+), 2 deletions(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 90e5790c318f..df71b057111b 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 +1542,11 @@ 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, +#ifdef CONFIG_USERFAULTFD + VM_FAULT_UFFD_MINOR =3D (__force vm_fault_t)0x008000, +#else + VM_FAULT_UFFD_MINOR =3D (__force vm_fault_t)0x000000, +#endif VM_FAULT_HINDEX_MASK =3D (__force vm_fault_t)0x0f0000, }; =20 @@ -1564,7 +1571,8 @@ enum vm_fault_reason { { VM_FAULT_FALLBACK, "FALLBACK" }, \ { VM_FAULT_DONE_COW, "DONE_COW" }, \ { VM_FAULT_NEEDDSYNC, "NEEDDSYNC" }, \ - { VM_FAULT_COMPLETED, "COMPLETED" } + { VM_FAULT_COMPLETED, "COMPLETED" }, \ + { VM_FAULT_UFFD_MINOR, "UFFD_MINOR" }, \ =20 struct vm_special_mapping { const char *name; /* The name, e.g. "[vdso]". */ 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 e16c7c8c3e1e..a9a31c0b5979 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