From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 1FBBD2798E8 for ; Tue, 9 Dec 2025 16:14:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765296860; cv=none; b=rDXTmOhstFBi6Vp8Qcy+3p/6ng5hOI3PnJsKkC9N/EzyrBTedbOCqvzZxN6wDVQhV3FZRp8uisLTlIB9gFXPPEg6mwQjMRZiAiUotOEPf1Z8qU8Hie6SBMzfPsdxde+ZuD9lYEirCFWlzF+LPiDGXx7Kez9TsvaEOTLffoAA0VM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765296860; c=relaxed/simple; bh=M8rFT9W0O1i0whoIsvepkLL7gueCl0KqPtNIjFdHObw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=e7gzImPMTUxbYuvnALPho4qy0qsek0UuHDgv+rDWOktZokm4OWusMkEKb8ZAyAfpiYiywZb8kwURG/6n49RJs86q/+i5GGdM2+TeQqJHowsH/WWYDwL1Ny0sfort2bI0P/VKfC2j1g6CIPpGlgRqbu+yA1OuQk0C83w74GFqABw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 2461A175D; Tue, 9 Dec 2025 08:14:10 -0800 (PST) Received: from [10.1.196.46] (e134344.arm.com [10.1.196.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1930E3F73B; Tue, 9 Dec 2025 08:14:13 -0800 (PST) Message-ID: <95c9947f-574a-486f-953c-fbac6ead0853@arm.com> Date: Tue, 9 Dec 2025 16:14:12 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 00/38] arm_mpam: Add KVM/arm64 and resctrl glue code To: Peter Newman Cc: James Morse , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, D Scott Phillips OS , carl@os.amperecomputing.com, lcherian@marvell.com, bobo.shaobowang@huawei.com, tan.shaopeng@fujitsu.com, baolin.wang@linux.alibaba.com, Jamie Iles , Xin Hao , dfustini@baylibre.com, amitsinght@marvell.com, David Hildenbrand , Dave Martin , Koba Ko , Shanker Donthineni , fenghuay@nvidia.com, baisheng.gao@unisoc.com, Jonathan Cameron , Gavin Shan , rohit.mathew@arm.com, reinette.chatre@intel.com, Punit Agrawal References: <20251205215901.17772-1-james.morse@arm.com> <41bcd0d2-d5b8-4f3d-b0b3-132387f547ed@arm.com> From: Ben Horgan Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Peter, On 12/9/25 15:53, Peter Newman wrote: > Hi Ben, > > On Tue, Dec 9, 2025 at 3:40 PM Ben Horgan wrote: >> >> Hi James and all, [...] >> >> One major departure from the previous snapshot branches referenced in >> the base driver series is that the same MPAM setting are used for >> kernel-space and user-space. That is, MPAM1_EL1 is set to the same value >> as MPAM0_EL1 rather than keeping the default value. The advantages of >> this are that it is closer to the x86 model where the closid is globally >> applicable, all partids are usable from user-space and user-space can't >> bypass MPAM controls by doing the work in the kernel. However, this >> causes some priority inversion where a high priority task waits to take >> a mutex held by another whose resources are restricted by MPAM. >> Thanks, > > In our experience, the disadvantages of the x86 model were worse > because they triggered on hosts unintentionally, while making the > kernel do work unrestricted on behalf of the user at least requires > intentional abuse. > > -Peter Thanks for the quick feedback. Do you have any more data/information on this that you can share? Thanks, Ben