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Peter Anvin" To: Andrew Cooper , 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, 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 Subject: =?US-ASCII?Q?Re=3A_=5BPATCHv6_00/16=5D_x86=3A_Enable_Lin?= =?US-ASCII?Q?ear_Address_Space_Separation_support?= User-Agent: K-9 Mail for Android In-Reply-To: <1aa5fb31-ce23-4c9f-ba1b-d5dc93402209@citrix.com> References: <61af62d9-4cd0-485f-8f0c-2da981f52695@intel.com> <1aa5fb31-ce23-4c9f-ba1b-d5dc93402209@citrix.com> Message-ID: <3DC9BFC2-1ABB-4486-A0E9-51786CF4FB58@zytor.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam02 X-Stat-Signature: rturxbkywdr5iofmta8zhyfus5ezzs3e X-Rspam-User: X-Rspamd-Queue-Id: F1D6D180011 X-HE-Tag: 1750459429-173136 X-HE-Meta: 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 ipmk/OFM ylpXcOE6GXODA9dvEwu7zpvql3kb5ReiND239fX6a9ETw+1jHQ9Aj7W5STqxU7rwHzzsx5HnXZrGs98cON2NiMmY6FjH+i9u7Vys6Gk+L0loNz6W8VE6l7uNEFh63WAuIh/m4d6FjZlMW4ICi8zBXWj1lKla/VPoUxi1SrB2KrxRzZPiwTtYwiCT6WT43eFLCAFiMC+NN7hU90gUn2JVH+NaeZ5ytgAxDoGpqfrhdFAL9iAQHMXh/0xSQ0wEOFbRhXLwEftCBA8wa7WXNzhGjWnBkM5scK5tUUhorKsfYbvLWviRka0/KbLasgnrJrulgm051NDQFeWSpTxdv5L2bqvB8daGZmtxBzjRFU1/Izdn6u11DEIHXVrpPBy3RBslKTZ8y1dL5RqywgszO5iJPtwBxmw/WWKrOdHiWASRg8NTd6QgehPecJGRfsABbRHHRIk7Y X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On June 20, 2025 3:04:53 PM PDT, Andrew Cooper wrote: >> Most of the cover letter here reads like an Intel whitepaper=2E 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=2E >> >> Could we say this up front in a prominent place, please? > >I'm going to nitpick=2E :) > >Yes, LASS would have made Meltdown a far less major problem than it was, >but I don't think that phrasing is fair=2E=C2=A0 As I recall, LASS was >literally invented as a "what would have been useful?" exercise in the >wake of Meltdown=2E > >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=2E > >Other things which would have helped would have been PKS (and this *was* >asked for ahead of Skylake launching=2E=2E=2E) > >The other important thing about LASS is that it does cut off a whole >class of sidechannels=2E=C2=A0 This halts definitely-rogue speculation, b= ut is >useful for non-speculative security too=2E > >~Andrew To some degree, the best way to describe LASS is "KPTI in hardware=2E" No,= it isn't an exact analogy =E2=80=93 we don't switch the entire page table = structure =E2=80=93 but it does make the supervisor page table structure pr= otected from user space *while still in memory*=2E It is coarser-grained than software KPTI, but on the other hand the separa= tion is absolute; there is to keep things like the kernel stack, descriptor= tables and entry/exit code unprotected=2E