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 E319E10970 for ; Wed, 29 Nov 2023 06:31:27 +0000 (UTC) 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 Authentication-Results: smtp.subspace.kernel.org; dkim=none 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 2944D1FB; Tue, 28 Nov 2023 22:32:14 -0800 (PST) Received: from [10.163.33.248] (unknown [10.163.33.248]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8497C3F6C4; Tue, 28 Nov 2023 22:31:21 -0800 (PST) Message-ID: <083c8502-9a0d-4876-b60a-bc26bb2ebabf@arm.com> Date: Wed, 29 Nov 2023 12:01:18 +0530 Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/3] arm64: Drop support for VPIPT i-cache policy Content-Language: en-US To: Marc Zyngier , kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org Cc: Will Deacon , Catalin Marinas , Mark Rutland , Ard Biesheuvel , James Morse , Suzuki K Poulose , Oliver Upton , Zenghui Yu References: <20231127172613.1490283-1-maz@kernel.org> From: Anshuman Khandual In-Reply-To: <20231127172613.1490283-1-maz@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/27/23 22:56, Marc Zyngier wrote: > ARMv8.2 introduced support for VPIPT i-caches, the V standing for > VMID-tagged. Although this looks like a reasonable idea, no > implementation has ever made it into the wild. > > Linux has supported this for over 6 years (amusingly, just as the > architecture was dropping support for AVIVT i-caches), but we had no > way to even test it, and it is likely that this code was just > bit-rotting. > > However, in a recent breakthrough (XML drop 2023-09, tagged as > d55f5af8e09052abe92a02adf820deea2eaed717), the architecture has > finally been purged of this option, making VIPT and PIPT the only two > valid options. Indeed, FEAT_VPIPT has been dropped from the 2023-09 document release. https://developer.arm.com/documentation/ddi0601/2023-06/AArch64-Registers/CTR-EL0--Cache-Type-Register CTR_EL0.L1Ip[15:14] = 00 - VMID aware Physical Index, Physical tag (VPIPT) with FEAT_VPIPT https://developer.arm.com/documentation/ddi0601/2023-09/AArch64-Registers/CTR-EL0--Cache-Type-Register CTR_EL0.L1Ip[15:14] = 00 - Reserved.