From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 12D3CEFCD99 for ; Mon, 9 Mar 2026 11:48:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:MIME-Version:References:In-Reply-To:Message-ID:Subject:CC:To: From:Date:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=XPVsGsLAQYthUlQ+IF2uVZCxwRhh5iC844+dcb8g99U=; b=oJS3J8d1DL5ox1lfxGsut8LXxX rkKTmtc+mAxQZ/ilKjYsHN2ssY8dWvTGGQ1E8g8BPd5z2/dAyp+8TKtW4t95wMOqxc+R4Py6rfL8W ocKmBDt4NN/TyZ/+HbJoP/RN8Juaog4w+Mj3OhtW5iUcr0aMufFcRXHMdez/AFutOMAfZfjR4MI+V DmHhmcoxYTZJh+8Ymfmskt+1+eyXAxuWSdBxRH9Hac6fE5ul3Vag8Mw2VkEF27BSJEB6wTLuUAKaP edVzvpnU12baibCgS6N2n/PG05RC8J8h4bjGd6wjHt5ORgThCrCdcz8/NJxxmGlWHONcwN+lyhe6O gA11MYZA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vzZ6N-00000007E2e-2rDx; Mon, 09 Mar 2026 11:48:47 +0000 Received: from frasgout.his.huawei.com ([185.176.79.56]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vzZ6K-00000007E2G-29mV for linux-arm-kernel@lists.infradead.org; Mon, 09 Mar 2026 11:48:46 +0000 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) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.203.177.15] X-ClientProxiedBy: lhrpeml500012.china.huawei.com (7.191.174.4) To dubpeml500005.china.huawei.com (7.214.145.207) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260309_044844_725210_2ECC16DF X-CRM114-Status: GOOD ( 13.86 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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