From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 3550D49691A for ; Mon, 11 May 2026 18:41:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=13.77.154.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778524879; cv=none; b=UBcprtT5bnq5z1or0+vqkXk/rwo7GX88ox8noqa+VvYDFIl1BIJ+8n6DAt3WK9n0tlhDEWJH9uuIPB7DKf9X0RbmxKiW9t4tdPXP+ySWn8W2qrl9N5+dJPEnzEb4U6L/CY1Z0Thhjd1qjUo2QCclnIKiwshhlG2hG7/RQFoRQlc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778524879; c=relaxed/simple; bh=9G5drU8uudnQcM5tFoq1RT6E6DRonPchxod+HcRURNs=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=SnZASaZey0HHn0NYnB4nE24IHrc4nc1MqJL6X+zPMNTz9I+jnbrV4f6iu/yUugdVQVLlDMsEO80xB+8HTwcTgZRISLbi0gDENCrZE7f2+xai+vJPaFODlmSnPKSu/BbdyCR7hDx0FasvO+ZSlReZf2Yjgm3hqMy4u3dC0SPc05g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com; spf=pass smtp.mailfrom=linux.microsoft.com; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b=eiV+hN+t; arc=none smtp.client-ip=13.77.154.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="eiV+hN+t" Received: from administrator-PowerEdge-R660.corp.microsoft.com (unknown [131.107.147.7]) by linux.microsoft.com (Postfix) with ESMTPSA id 3332320B7166; Mon, 11 May 2026 11:41:15 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 3332320B7166 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1778524875; bh=4UPwngaq0K4b1+zPxzFk/s8xH///9M8W01sYkypT5J4=; h=From:To:Cc:Subject:Date:From; b=eiV+hN+tcQunxmAcOFaRrB/ErxKDHMWO+4Iq0rX6S4KwC8XzwZTGDi+XnF1JmrBcX u4OdURYsLLSzj4QWnFXsooAev11TaWVbs17F6n/yZ66KygJqNgVSxVpgO1k9V4UXvS /Xfn2gB0yVZvLTDQRjnrg5vmcOklZsQ25xC5fAYk= From: Jacob Pan To: linux-kernel@vger.kernel.org, "iommu@lists.linux.dev" , Jason Gunthorpe , Alex Williamson , Joerg Roedel , Mostafa Saleh , David Matlack , Robin Murphy , Nicolin Chen , "Tian, Kevin" , Yi Liu Cc: Saurabh Sengar , skhawaja@google.com, pasha.tatashin@soleen.com, Will Deacon , Jacob Pan , Baolu Lu Subject: [PATCH v5 0/9] iommufd: Enable noiommu mode for cdev Date: Mon, 11 May 2026 11:41:05 -0700 Message-ID: <20260511184116.3687392-1-jacob.pan@linux.microsoft.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit VFIO's unsafe_noiommu_mode has long provided a way for userspace drivers to operate on platforms lacking a hardware IOMMU. Today, IOMMUFD also supports No-IOMMU mode for group-based devices under vfio_compat mode. However, IOMMUFD's native character device (cdev) does not yet support No-IOMMU mode, which is the purpose of this patch. In summary, we have: |-------------------------+------+---------------| | Device access mode | VFIO | IOMMUFD | |-------------------------+------+---------------| | group /dev/vfio/$GROUP | Yes | Yes | |-------------------------+------+---------------| | cdev /dev/vfio/devices/ | No | This patch | |-------------------------+------+---------------| Beyond enabling cdev for IOMMUFD, this patch also addresses the following deficiencies in the current No-IOMMU mode suggested by Jason[1]: - Devices operating under No-IOMMU mode are limited to device-level UAPI access, without container or IOAS-level capabilities. Consequently, user-space drivers lack structured mechanisms for page pinning and often resort to mlock(), which is less robust than pin_user_pages() used for devices backed by a physical IOMMU. For example, mlock() does not prevent page migration. - There is no architectural mechanism for obtaining physical addresses for DMA. As a workaround, user-space drivers frequently rely on /proc/pagemap tricks or hardcoded values. By allowing noiommu device access to IOMMUFD IOAS and HWPT objects, this patch brings No-IOMMU mode closer to full citizenship within the IOMMU subsystem. In addition to addressing the two deficiencies mentioned above, the expectation is that it will also enable No-IOMMU devices to seamlessly participate in live update sessions via KHO [2]. Furthermore, these devices will use the IOMMUFD-based ownership checking model for VFIO_DEVICE_PCI_HOT_RESET, eliminating the need for an iommufd_access object as required in a previous attempt [3]. ChangeLog: V5: - Split CONFIG_VFIO_NOIOMMU into CONFIG_VFIO_GROUP_NOIOMMU and CONFIG_VFIO_CDEV_NOIOMMU so cdev noiommu is independent of VFIO_GROUP (Alex) - Add CAP_SYS_RAWIO check for cdev open and bind under noiommu, security parity with group noiommu (Alex) - Add IS_ENABLED(CONFIG_IOMMUFD_NOIOMMU) guard in iommufd_device_is_noiommu() to prevent noiommu bind when feature is disabled - Add prep patch to tolerate NULL group for cdev noiommu devices when CONFIG_VFIO_GROUP_NOIOMMU is not set [7/9] - Rename IOCTL to IOMMUFD_CMD_IOAS_NOIOMMU_GET_PA to be more specific (Kevin) - Simplify iommufd_device_is_noiommu, use iommufd_bind_noiommu helper (Kevin, Yi) - Move IOMMU cap check under iommufd_bind_iommu() (Yi) - Fix next_iova exceeding iopt_area_last_iova in GET_PA (Alex) - Fix const hwpt, copyright date, typo in moved comment (Kevin) - Add Reviewed-by tags - Squash noiommu cdev selftest fix into selftest patch - Drop DSA selftest patch - Details in each patch changelog. V4: - Fix various corner cases pointed out by (Sashiko) Details in each patch changelog. V3: - Improve error handling [3/10] (Mostafa) - Simplify vfio_device_is_noiommu logic and merged in [6/10] (Mostafa) - Add comment to explain the design difference over the legacy noiommu VFIO code.[1/10] V2: - Fix build dependency by adding IOMMU_SUPPORT in [8/11] - Add an optimization to scan beyond the first page for a contiguous physical address range and return its length instead of a single page.[4/11] Since RFC[4]: - Abandoned dummy iommu driver approach as patch 1-3 absorbed the changes into iommufd. [1] https://lore.kernel.org/linux-iommu/20250603175403.GA407344@nvidia.com/ [2] https://lore.kernel.org/linux-pci/20251027134430.00007e46@linux.microsoft.com/ [3] https://lore.kernel.org/kvm/20230522115751.326947-1-yi.l.liu@intel.com/ [4] https://lore.kernel.org/linux-iommu/20251201173012.18371-1-jacob.pan@linux.microsoft.com/ Future cleanup: consolidate all CONFIG_IOMMUFD_NOIOMMU code (iopt_get_phys, iommufd_ioas_noiommu_get_pa, iommufd_noiommu_ops) into hwpt_noiommu.c to eliminate #ifdef guards from ioas.c and io_pagetable.c. Signed-off-by: Jacob Pan -- 2.43.0