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 1F6D34014BA; Mon, 2 Mar 2026 14:54:36 +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=1772463280; cv=none; b=DoH51BtAD7ep6HSQ9dHlB2SudktPBKB/FSGecM1YeKph4u4bhZ/uf9xu72oIQPqJuW0vondeijSHbvrjgn4PSSqoIu2vGq9PumCv7L7CLH+Z3I/60zVOAkc47KYRN2tAlz7wG68FixFu/rxLZ7KHy2eA/aOY6cX/qd9uQ66lv20= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772463280; c=relaxed/simple; bh=PWWbqj84w74ygfO+gwepT4UHsgScdDpJJQmJM9KjRTc=; h=Date:From:To:CC:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=r3+viKtVAG2aI1s5l+588PVcSy+hCHGrIO0cAKEXZAvLvFtePPfQGlMin08gjfBLWsq3Zn24fPSOJgqu3uW+xJBF1dgMnik5uFO0eMJqGOGK9hB6lDg6UuBpRsZeW4k+FOqaSV9cSUaTcDQnIQtYalPz4qQ6RWlYtarPmu7SvrA= 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 [172.18.224.83]) 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) Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: lhrpeml500009.china.huawei.com (7.191.174.84) To dubpeml500005.china.huawei.com (7.214.145.207) 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 >