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 58F5CCA5FD2 for ; Thu, 1 Oct 2026 16:00:52 +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:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=l32CwL6RPdOm0EOwrBJy8YAfpk95iBBbK/6pVfpnLNs=; b=YOJbCGanheiaNtRZPRQDO7YR4N mvKuDpD16YAZEAIVXQTBCalM47NBTe43C+WZigXHgjjbL3Mwkt+frfqwy0aZtm1wI4iUvPFTkQC9j iH2g51eYwIZOeBdSkK9x4b97yWWmfcpAtkFPwT+xTrMuUmdyjQH5siMEPFNS55bJISBoJanTT1EY9 uBvIiwuLGhf6GyUO84y2wuD0Tu4U9bGF52FTiMgH8s4z05T/MgVI63PfQrUNpyKkDPAUZ35kbWGGU utAFgWEk4KxmiaOsP614z3swLVHgKTvfwuc6HSZFRF2oPTP4GEl5cviV9JCktJfeGpntmhlbM5z4v miig30Mw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xCJD1-00000009cwJ-33xv; Thu, 01 Oct 2026 16:00:39 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xCJCq-00000009ctn-3ABb for linux-arm-kernel@lists.infradead.org; Thu, 01 Oct 2026 16:00:30 +0000 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 1FEC4497; Thu, 1 Oct 2026 09:00:20 -0700 (PDT) Received: from arm.com (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C3D223F86F; Thu, 1 Oct 2026 09:00:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1790870423; bh=0anjATVLl2lFF6xlG/CGUPt6vidLI3eT3YTi5MQ///E=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=G3xWRSBQWtIqgglyOJmaSWMX/UDPwmvoExYNxIE0ePHLzqcWUzcwVZv1byOMMam6F BlWIyCHOtKna0FkFlcn0tMPdzXPBFB0xm9fjDAkBMrZWqxVeLGRUfe2Xt/5+PchBwC uoDb3hZ+SDpHJdALdRv8yXyTynyk3G2mqkOJJY5w= Date: Thu, 1 Oct 2026 17:00:15 +0100 From: Catalin Marinas To: Fuad Tabba Cc: Will Deacon , Mark Rutland , Jonathan Corbet , Shuah Khan , Randy Dunlap , Ben Horgan , James Morse , Xi Ruoyao , Marc Zyngier , Bradley Morgan , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] arm64: mpam: Document when to set arm64.nompam Message-ID: References: <20260908145622.2828319-1-fuad.tabba@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261001_090026_739205_4DB4B4E3 X-CRM114-Status: GOOD ( 18.27 ) 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 Mon, Sep 28, 2026 at 07:56:14AM +0100, Fuad Tabba wrote: > On Tue, 8 Sept 2026 at 15:56, Fuad Tabba wrote: > > arm64.nompam skips the MPAM2_EL2 and MPAMHCR_EL2 writes in > > finalise_el2_state and leaves the ARM64_MPAM cpucap unset. Where EL3 > > firmware has cleared MPAM3_EL3.TRAPLOWER, the EL2 trap controls are > > left unwritten, at reset values that are UNKNOWN, and KVM still hides > > MPAM from the guest but no longer enables the traps that stop a guest > > from using it. KVM never saves or restores MPAM0_EL1, MPAM1_EL1 and > > MPAMSM_EL1, so what one guest writes reaches the next guest and the > > host. Nor can the kernel make the EL2 writes unconditionally: they trap > > to EL3 on the firmware the option exists for, and TRAPLOWER cannot be > > read below EL3. > > > > Say so in mpam.rst, and add the rule and a pointer to the > > kernel-parameters entry. > > Gentle ping on this one; it has Ben's and Bradley's R-b. I think it > still stands regardless of the other cpufeature work going on now. > Anything else needed for it to go in? Normally I expect a pull request from Ben or James but they rarely send one in time ;). I'll apply it directly. -- Catalin