From nobody Sun Feb 8 21:33:55 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 0D2DB2BCF7F; Tue, 27 Jan 2026 19:31:03 +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=1769542263; cv=none; b=X04DsPDIwsdAoA7HU/u/h0O37C8c/x/vH48iGJe7ex+Y+uJQcS9PhAHKUjgi3TS7ZsCGRWgSmFHsZqAJYzemE5+edu200QrJ4vBTaxFarpZJwsotE8p8uqiXJCLK6IJnGcg6gQs3OJaHYX87uqP03F2tCRaejwEdR0e2deVXr3E= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769542263; c=relaxed/simple; bh=h+TcgWCVPD30aK45h+wpUIJypZftXhAg5ucXDIazF9Y=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=D1B83Sg6OZEo5j58Fw/L9NN270Vzf/hmSuUmjTERsSUmidldnyQlWRlw1FotSUAOjy4TQN9jD8/DkZEldk0RTa6bvlr1+YstJzVf52n7uq1AZyY3gHE6jxDljHxZNE7esaveZERCOhPLXkO9La/skurdh7Y+AG3114L/1qcHXpw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=q2UsiRPu; 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="q2UsiRPu" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F19B2C116C6; Tue, 27 Jan 2026 19:30:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1769542262; bh=h+TcgWCVPD30aK45h+wpUIJypZftXhAg5ucXDIazF9Y=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=q2UsiRPuaj/8L0lU3PZimX+KdU+NnUJ4T6kgHnK7oKJ7dnF20S1Wu60dtz3r+KU1H 0T+7qAEjj3JbVgEGy3R0Hx3DRfjX2B6I9PzRs1e6vap8/WGmkswqz84raN0EuooQAV 5E4A1pVzNprdPWdgwAmWXAr69bCVgPHlBxziKewff7xctTxCeA2TMO1wQzD8XqEI6f Ed4jSaIIhYNV6/OJpzSKzJ1lZMwUBOT5T1blV/qYiHyC03fgIpcZ1vmjVxxtXEnaon 0hSCYpfGeJVTvH9YpHOBZSgxib2aLHu9IQ7ZrqCo73Rgfq3eGnPiCbchrIFCt6eypg 1wteWBH/FqJkQ== 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, "David Hildenbrand (Red Hat)" Subject: [PATCH RFC 12/17] mm: introduce VM_FAULT_UFFD_MINOR fault reason Date: Tue, 27 Jan 2026 21:29:31 +0200 Message-ID: <20260127192936.1250096-13-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: "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_MINOR). 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_MINOR) to complete a page fault. Replace a call to handle_userfault(VM_UFFD_MINOR) 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: Nikita Kalyazin Signed-off-by: Mike Rapoport (Microsoft) --- include/linux/mm_types.h | 10 +++++++++- mm/memory.c | 5 ++++- mm/shmem.c | 2 +- 3 files changed, 14 insertions(+), 3 deletions(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 42af2292951d..b25ac322bfbf 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -1555,6 +1555,8 @@ 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 * */ @@ -1572,6 +1574,11 @@ 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 @@ -1596,7 +1603,8 @@ 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 2a55edc48a65..fcb3e0c3113e 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -5319,8 +5319,11 @@ 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_DONE_COW | VM_FAULT_UFFD_MINOR))) { + if (ret & VM_FAULT_UFFD_MINOR) + return handle_userfault(vmf, VM_UFFD_MINOR); return ret; + } =20 folio =3D page_folio(vmf->page); if (unlikely(PageHWPoison(vmf->page))) { diff --git a/mm/shmem.c b/mm/shmem.c index 6f0485f76cb8..6aa905147c0c 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2481,7 +2481,7 @@ 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 2.51.0