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[92.26.98.202]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a6d1188247sm3046998f8f.76.2025.06.20.15.04.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 20 Jun 2025 15:04:55 -0700 (PDT) Message-ID: <1aa5fb31-ce23-4c9f-ba1b-d5dc93402209@citrix.com> Date: Fri, 20 Jun 2025 23:04:53 +0100 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird To: dave.hansen@intel.com Cc: acme@redhat.com, aik@amd.com, akpm@linux-foundation.org, alexander.shishkin@linux.intel.com, ardb@kernel.org, ast@kernel.org, bp@alien8.de, brijesh.singh@amd.com, changbin.du@huawei.com, christophe.leroy@csgroup.eu, corbet@lwn.net, daniel.sneddon@linux.intel.com, dave.hansen@linux.intel.com, ebiggers@google.com, geert+renesas@glider.be, houtao1@huawei.com, hpa@zytor.com, jgg@ziepe.ca, jgross@suse.com, jpoimboe@kernel.org, kai.huang@intel.com, kees@kernel.org, kirill.shutemov@linux.intel.com, leitao@debian.org, linux-doc@vger.kernel.org, linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux@rasmusvillemoes.dk, luto@kernel.org, mcgrof@kernel.org, mhiramat@kernel.org, michael.roth@amd.com, mingo@kernel.org, mingo@redhat.com, namhyung@kernel.org, paulmck@kernel.org, pawan.kumar.gupta@linux.intel.com, peterz@infradead.org, rick.p.edgecombe@intel.com, rppt@kernel.org, sandipan.das@amd.com, shijie@os.amperecomputing.com, sohil.mehta@intel.com, tglx@linutronix.de, tj@kernel.org, tony.luck@intel.com, vegard.nossum@oracle.com, x86@kernel.org, xin3.li@intel.com, xiongwei.song@windriver.com, ytcoode@gmail.com References: <61af62d9-4cd0-485f-8f0c-2da981f52695@intel.com> Subject: Re: [PATCHv6 00/16] x86: Enable Linear Address Space Separation support Content-Language: en-GB From: Andrew Cooper Autocrypt: addr=andrew.cooper3@citrix.com; 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charset=UTF-8 Content-Transfer-Encoding: 8bit > Most of the cover letter here reads like an Intel whitepaper. That's not > the worst thing in the world, but I think it glosses over one very > important point: > > Had it been available, LASS alone would have mitigated Meltdown. > > Could we say this up front in a prominent place, please? I'm going to nitpick. :) Yes, LASS would have made Meltdown a far less major problem than it was, but I don't think that phrasing is fair.  As I recall, LASS was literally invented as a "what would have been useful?" exercise in the wake of Meltdown. However, a less well known/researched area of Meltdown, which would not be addressed by LASS, is the ability to pend stores to read-only memory and proceed with the expectation that they'll success. Other things which would have helped would have been PKS (and this *was* asked for ahead of Skylake launching...) The other important thing about LASS is that it does cut off a whole class of sidechannels.  This halts definitely-rogue speculation, but is useful for non-speculative security too. ~Andrew