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 4AC44C9830D for ; Fri, 25 Sep 2026 09:26:42 +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:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=LiQa2P0K09njvbQ2YQr3gPhYTEh8ecgaEVkM4ZtaZMs=; b=z3Fh5qp/zcpUzjZW4uSwEh7Pxs J038MRmxJ7Nr2X4rAi7Yx8oVTfpJ6nbmpipV/oySr+PsM91jdpsMOd9LIENDrp5Vav3hMwmMhLMgm IDh+Y1NRv6CffrEkbCtprTNIXRYc04l5jnq4NooQoJWgRwhs1aKDK2vLaCawDQmaGtE7u2pQ8LS2l 6cXMIniiufe29oO1zTqdNFVw/tesyCUEA0T0SN1ujfStga2ZndcFXwHv5WC7e+qdQPSxxTdCK5W3l y+pMhgm+G4EhpoGzc2leLzYswNhQ114rmin/mDr2oH2aPTOwKfO/J8pxMrDRSlp37Tbsy7XOBgKLm LNYE7LsA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1xA2CQ-0000000Czgf-10HZ; Fri, 25 Sep 2026 09:26:34 +0000 Received: from desiato.infradead.org ([2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1xA2CO-0000000CzgT-2qBW for linux-arm-kernel@bombadil.infradead.org; Fri, 25 Sep 2026 09:26:32 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=Content-Transfer-Encoding:Content-Type :In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date:Message-ID: Sender:Reply-To:Content-ID:Content-Description; bh=LiQa2P0K09njvbQ2YQr3gPhYTEh8ecgaEVkM4ZtaZMs=; b=PFISGUjpapQbsHDTAHBX1K2h3R PBoMTgIFv/Ny1rhoDUEiTlKkKyPEx+09sYCtNr5GWpi6WWD5AnKbUsjWDGxdD3OLIx4V1uLVs5mPn tX4x2LJxitw+j3VHJC86vQEtXmiUaslAf1YnP9hSHApggVFo+8aiir7o08jaKlpcd2TrxhES/t9HF P5vn+KqWFID+pNavsF+dCkPPYbqwYA9twDby7K7Gpvc9v+FqEucoUHUICZMGCuPmjfwCCod+yNPPs qh3gjS6xnfQOM3spXvCEWLE2dIznBalxmhSdE0xde4qJgQFzzF2snQ7gC3WQvH1QbndGFyp6+sX08 5YdEcwew==; Received: from foss.arm.com ([217.140.110.172]) by desiato.infradead.org with esmtp (Exim 4.99.2 #2 (Red Hat Linux)) id 1xA2CL-0000000GlbP-0J0W for linux-arm-kernel@lists.infradead.org; Fri, 25 Sep 2026 09:26:31 +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 96F3C1688; Fri, 25 Sep 2026 02:26:23 -0700 (PDT) Received: from [10.2.212.8] (e134344.arm.com [10.2.212.8]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 23B893F86C; Fri, 25 Sep 2026 02:26:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1790328387; bh=3kjd6lZj1dIUtedJktMj1UoleqR9/JbTLWiLSRcewj4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=TG6UsdHMPSeGq8RWseV0KrNzFW1yYNZcoAhoPJb+pCuWrkSYVje8gJNRx200IDpVW AFFAKsMlumA3VQnJEnAvDx8FX7Sjjgm2LcTqHUMe/7RhcQzVIqgB7be3ZWQudoZp4v jjROSC6mVXc8ucrhayAS/kPSypertZMowkz/8mu4= Message-ID: Date: Fri, 25 Sep 2026 10:26:23 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] arm64: mpam: Document when to set arm64.nompam To: Fuad Tabba , Catalin Marinas , Will Deacon Cc: Mark Rutland , Jonathan Corbet , Shuah Khan , Randy Dunlap , James Morse , Xi Ruoyao , Marc Zyngier , Bradley Morgan , Fuad Tabba , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260908145622.2828319-1-fuad.tabba@linux.dev> Content-Language: en-US From: Ben Horgan In-Reply-To: <20260908145622.2828319-1-fuad.tabba@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260925_102629_456552_3AD6B39F X-CRM114-Status: GOOD ( 11.45 ) 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 Hi Fuad, On 08/09/2026 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. > > Suggested-by: Ben Horgan > Link: https://lore.kernel.org/all/CA+EHjTxeWxZiuSmnKLGLxTBXP4oJT7-LuffbPAyCSZZ5TW=5Ew@mail.gmail.com/ > Reviewed-by: Bradley Morgan > Signed-off-by: Fuad Tabba Reviewed-by: Ben Horgan Thanks, Ben