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 BF7E725522B; Tue, 25 Mar 2025 11:06:48 +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=1742900811; cv=none; b=eyX/XmQ18YEso8BFOIocySL2TeCURhoxcA1nLvY0a2TnKEA4LVv71smZX0ZvEglIAVOkDTeR0VZhiYG3nvtiTLPZ7HtsIjWN7V2GQdIz4se+YREwzxSr8XfRTvVS8G0Op+tciogrwcwpr/bP6CIbJFK/SQIyUT7phUDekjzf0N8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742900811; c=relaxed/simple; bh=1oUtFGtYzogbL0vB7U/WIQ8hwYhjr5hl5aNe3i3p1t8=; h=Message-ID:Date:MIME-Version:Subject:To:References:From: In-Reply-To:Content-Type; b=nArYDGCp7u9DRk7Mmo/soWcrNfqm+6QpP06qsP7H5N0vprGKzBhi/TaknNrM5N4xrRT8B2je8IYMCr8782s8ezoFuFKmxgbrVAlh58ibET+KJjBqcjEIlO+XqFQBJo0+NUZUpbHGdxTdaNqJ+Is/LlXVA869m2H3OND6l8QN+io= 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 4D407106F; Tue, 25 Mar 2025 04:06:48 -0700 (PDT) Received: from [10.1.197.1] (ewhatever.cambridge.arm.com [10.1.197.1]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 182383F58B; Tue, 25 Mar 2025 04:06:38 -0700 (PDT) Message-ID: <5e49377e-6a3e-4a48-94c9-db06f13cffe8@arm.com> Date: Tue, 25 Mar 2025 11:06:37 +0000 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 1/3] arm64: Add BBM Level 2 cpu feature To: =?UTF-8?Q?Miko=C5=82aj_Lenczewski?= , ryan.roberts@arm.com, yang@os.amperecomputing.com, corbet@lwn.net, catalin.marinas@arm.com, will@kernel.org, jean-philippe@linaro.org, robin.murphy@arm.com, joro@8bytes.org, akpm@linux-foundation.org, ardb@kernel.org, mark.rutland@arm.com, joey.gouly@arm.com, maz@kernel.org, james.morse@arm.com, broonie@kernel.org, oliver.upton@linux.dev, baohua@kernel.org, david@redhat.com, ioworker0@gmail.com, jgg@ziepe.ca, nicolinc@nvidia.com, mshavit@google.com, jsnitsel@redhat.com, smostafa@google.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev References: <20250325093625.55184-1-miko.lenczewski@arm.com> <20250325093625.55184-2-miko.lenczewski@arm.com> Content-Language: en-US From: Suzuki K Poulose In-Reply-To: <20250325093625.55184-2-miko.lenczewski@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 25/03/2025 09:36, Mikołaj Lenczewski wrote: > The Break-Before-Make cpu feature supports multiple levels (levels 0-2), > and this commit adds a dedicated BBML2 cpufeature to test against > support for, as well as a kernel commandline parameter to optionally > disable BBML2 altogether. > > This is a system feature as we might have a big.LITTLE architecture > where some cores support BBML2 and some don't, but we want all cores to > be available and BBM to default to level 0 (as opposed to having cores > without BBML2 not coming online). > > To support BBML2 in as wide a range of contexts as we can, we want not > only the architectural guarantees that BBML2 makes, but additionally > want BBML2 to not create TLB conflict aborts. Not causing aborts avoids > us having to prove that no recursive faults can be induced in any path > that uses BBML2, allowing its use for arbitrary kernel mappings. > Support detection of such CPUs. > > Signed-off-by: Mikołaj Lenczewski Reviewed-by: Suzuki K Poulose