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 1B66EEA4E04 for ; Mon, 2 Mar 2026 14:54:42 +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=P1zRTXmeQCbtkPZiqRqHWxQMxoWFGt3hTwtVnY/mfXE=; b=FauXAiRxC+niBDC8nOHPPfMRMZ MmDpd18IrGh5/qi4ytmgfevi+gHKnduaG65YXE7y62IpzxSr+qUE1H3PG4HjRakzbhAhvr3fZetii ynkub7kjXuUUqP5IQ3H9c6kIMBv4M3paYHXLd5JVdHB7rMf9GLU+EbXGXsGIHhN/tD77W7wCQazo+ /pAy3xzuxzexlhrYJDT2xtEwjzIoLyf0Po3BWOM7NKFlPGPF/mIjPz/HePzuwLXD38T5NBbegaTHl qkjLvRz7E3WgogOBKndk7/DDfoGDNTJUGo6f9kOIdA5FQS16OqusOvLtWhvo0eyq4NX8YTvP7cYcR s9v1Gf0g==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vx4fM-0000000DGlp-0YyS; Mon, 02 Mar 2026 14:54:36 +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 1vx4fJ-0000000DGlQ-03SH for linux-arm-kernel@lists.infradead.org; Mon, 02 Mar 2026 14:54:34 +0000 Received: from mail.maildlp.com (unknown [172.18.224.83]) by frasgout.his.huawei.com (SkyGuard) with ESMTPS id 4fPhl51Y1VzHnGdP; Mon, 2 Mar 2026 22:53:37 +0800 (CST) Received: from dubpeml500005.china.huawei.com (unknown [7.214.145.207]) by mail.maildlp.com (Postfix) with ESMTPS id 2C32140086; Mon, 2 Mar 2026 22:54:29 +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, 2 Mar 2026 14:54:28 +0000 Date: Mon, 2 Mar 2026 14:54:26 +0000 From: Jonathan Cameron To: Jason Gunthorpe CC: Nicolin Chen , , , , , , , , , , , , , Subject: Re: [PATCH v2 3/3] iommu/arm-smmu-v3: Allow ATS to be always on Message-ID: <20260302145426.00001960@huawei.com> In-Reply-To: References: <20260224120615.00003ad9@huawei.com> <20260224155742.00000282@huawei.com> 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: lhrpeml500009.china.huawei.com (7.191.174.84) 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-20260302_065433_208886_4304D9B1 X-CRM114-Status: GOOD ( 19.43 ) 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 Tue, 24 Feb 2026 12:09:47 -0400 Jason Gunthorpe wrote: > On Tue, Feb 24, 2026 at 03:57:42PM +0000, Jonathan Cameron wrote: > > On Tue, 24 Feb 2026 10:51:02 -0400 > > Jason Gunthorpe wrote: > > > > > On Tue, Feb 24, 2026 at 12:06:15PM +0000, Jonathan Cameron wrote: > > > > > > > In my head at least, it would be nice if a driver had to explicitly opt in > > > > to this behavior. The presence of CXL.cache support for instance doesn't > > > > actually mean the driver is going to enable it. However it is probably > > > > harmless so lets go with this as path of least resistance. > > > > > > That same remark applies to ATS in general, we have no idea if the > > > device is going to use it when turned on or not.. > > > > Yup. Understood. That's the bit that smells bad to me. > > Do you have thoughts on when this is a problem (aside from device > pre-acceptance security already discussed)? So far I haven't heard > complaining on this point.. Nothing explicit. It was a very minor smells wrong moan on basis of assumptions of what an IOMMU is doing in the way of ATS checking if we have a malicious device. So principle of not turning anything on we don't know we need. Jonathan > > Jason >