From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) (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 C2AEC39B4BA for ; Mon, 9 Mar 2026 11:48:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.176.79.56 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773056924; cv=none; b=anb48z3ibR1hoWlDnzBVmJRPJH3KyEoVR40yWQkWXultdPsbNnBs8fwJZtXAUxgYqDbaZ8MjAJCIrbtzGKi4oBn/GPKnbeF4PNeRk4Ydx+k6DWcnIrKULEjQ1uPElg/Q4Ze1N4p7Va6sXbPLz7eSFVPZG5SiKYG/gBqVdAJuoJs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773056924; c=relaxed/simple; bh=UocW/bVxbkC7JT72bY+HpzTQxEjsiiz6KerJNocdQ6o=; h=Date:From:To:CC:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=Tc8zJufTJgQuI4+s8lpF491onb6LO8JIcxmq0i9SP1ez5Nc3TWvNadi0OTRa40GLUyA4npp7wyHC1ZbKR+82zm4nMMs9ILWGfLrJoDt4z/+bhqR4CV9eQDUUXfOUUvYctaJULz1o6pWcPSzMPtyu3uSzqFpRgixIK+eLHAInnfA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=185.176.79.56 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.18.224.107]) by frasgout.his.huawei.com (SkyGuard) with ESMTPS id 4fTwHZ4drZzJ46vg; Mon, 9 Mar 2026 19:47:54 +0800 (CST) Received: from dubpeml500005.china.huawei.com (unknown [7.214.145.207]) by mail.maildlp.com (Postfix) with ESMTPS id 815B940584; Mon, 9 Mar 2026 19:48:37 +0800 (CST) Received: from localhost (10.203.177.15) by dubpeml500005.china.huawei.com (7.214.145.207) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Mon, 9 Mar 2026 11:48:36 +0000 Date: Mon, 9 Mar 2026 11:48:35 +0000 From: Jonathan Cameron To: Nicolin Chen CC: , , , , , , , , , , , , , , , Subject: Re: [PATCH v3 1/3] PCI: Allow ATS to be always on for CXL.cache capable devices Message-ID: <20260309114835.000051c9@huawei.com> In-Reply-To: References: X-Mailer: Claws Mail 4.3.0 (GTK 3.24.42; x86_64-w64-mingw32) Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: lhrpeml500012.china.huawei.com (7.191.174.4) To dubpeml500005.china.huawei.com (7.214.145.207) On Fri, 6 Mar 2026 15:41:15 -0800 Nicolin Chen wrote: > Controlled by the IOMMU driver, ATS is usually enabled "on demand" when a > device requests a translation service from its associated IOMMU HW running > on the channel of a given PASID. This is working even when a device has no > translation on its RID (i.e., the RID is IOMMU bypassed). > > However, certain PCIe devices require non-PASID ATS on their RID even when > the RID is IOMMU bypassed. Call this "always on". > > For instance, the CXL spec notes in "3.2.5.13 Memory Type on CXL.cache": > "To source requests on CXL.cache, devices need to get the Host Physical > Address (HPA) from the Host by means of an ATS request on CXL.io." > > In other words, the CXL.cache capability requires ATS; otherwise, it can't > access host physical memory. > > Introduce a new pci_ats_always_on() helper for the IOMMU driver to scan a > PCI device and shift ATS policies between "on demand" and "always on". > > Add the support for CXL.cache devices first. Pre-CXL devices will be added > in quirks.c file. > > Note that pci_ats_always_on() validates against pci_ats_supported(), so we > ensure that untrusted devices (e.g. external ports) will not be always on. > This maintains the existing ATS security policy regarding potential side- > channel attacks via ATS. > > Cc: linux-cxl@vger.kernel.org > Suggested-by: Vikram Sethi > Suggested-by: Jason Gunthorpe > Signed-off-by: Nicolin Chen Reviewed-by: Jonathan Cameron