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Thu, 27 Aug 2026 03:07:35 +0000 Message-ID: <0a66aeb1-30fd-4223-adae-a01bd77de8e7@intel.com> Date: Thu, 27 Aug 2026 11:07:28 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/5] target/i386: Add support for LASS To: Kishen Maloor , CC: , , , , , References: <20260826035734.114685-1-kishen.maloor@intel.com> Content-Language: en-US From: "Chen, Farrah" In-Reply-To: <20260826035734.114685-1-kishen.maloor@intel.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: TPYP295CA0006.TWNP295.PROD.OUTLOOK.COM (2603:1096:7d0:9::16) To SJ2PR11MB7504.namprd11.prod.outlook.com (2603:10b6:a03:4c5::7) Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH0PR11MB7494:EE_|SA3PR11MB192006:EE_ X-MS-Office365-Filtering-Correlation-Id: 9d33aab9-c5f9-48cb-fd0e-08df03e8572b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|366016|23010399003|1800799024|10067099003|56012099006|6133799003|11063799006|3023799007|22082099003|18002099003; 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Paging, > along with SMEP and SMAP, already provides mode-based access protection, > but enforcing it requires a page walk whose timing can leak the layout of > kernel memory. LASS applies the equivalent protections during > linear-address pre-processing: given the usual partitioning of the linear > address space into a user half (bit 63 clear) and a supervisor half > (bit 63 set), an access targeting the opposite half is rejected on the > basis of bit 63 alone, before any page walk. > > This series enumerates the LASS CPUID bit, recognizes CR4.LASS, > and exposes LASS on the relevant Intel CPU models via new versioned models. > LASS is not emulated by TCG. > > Exposing LASS to a guest also requires KVM support: KVM must validate > the CPUID bit and CR4.LASS, and enforce LASS violations in its > instruction emulator. That enabling is currently under review [2]. > I tested this series on Clearwater Forest (CWF), running a KVM guest with -cpu host. On the host I applied the KVM LASS enabling series referenced as [2] in the cover letter: https://lore.kernel.org/kvm/20260806011536.4172258-1-sohil.mehta@intel.com/ With both series applied, LASS is correctly enumerated in the guest, and the LASS functional tests pass with vsyscall=none/xonly/emulate. Tested-by: Farrah Chen