From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4971F19E98C; Fri, 20 Jun 2025 22:44:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750459448; cv=none; b=NYLrutn/mtKVt3UNkKuyLKR5UTLOGStfAiYNJaja8rt6m3aUIAkouwHmzQlWJZB70HVaD5zsTan9nNP3EEnzTrpoGVhT3QF/JyrFfUQeUPDkY4zK7xFvH2sBZBq06hcLxXQocvy8CKFuipnta45fy/dNqWeaS1SYuWPflpq5Tjw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750459448; c=relaxed/simple; bh=u5xl9aa54YjbWNHfmXDmbQh7jC2zVdtatoBtPEbVP1Q=; h=Date:From:To:CC:Subject:In-Reply-To:References:Message-ID: MIME-Version:Content-Type; b=OadjPISwdZXEb6emQocGTrwfvq5QQlAHijX202mI1pXKiJLrXc4J0CcNKq58S2Ssyh2GKaK7YpQdCi9AYXjDEcnXQ1kLD1AtJVSi259zlVu7l8vMHWGDk/pd9wI8I/vyeyVz1R0d1Zc2b+JB/M8GmL/zKyfynMEu67S2shG7soc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com; spf=pass smtp.mailfrom=zytor.com; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b=AfWpICZP; arc=none smtp.client-ip=198.137.202.136 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=zytor.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="AfWpICZP" Received: from [127.0.0.1] (c-76-133-66-138.hsd1.ca.comcast.net [76.133.66.138]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 55KMh1te2666944 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Fri, 20 Jun 2025 15:43:02 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 55KMh1te2666944 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2025052101; t=1750459385; bh=Ft7/uWL+enycBzUOY5QuCn/nDuBUXLYso8y0U0CAkl0=; h=Date:From:To:CC:Subject:In-Reply-To:References:From; b=AfWpICZPnnGxDHY/DhQUGSTLuPfinQE/Numg7yUAThjuFQvN0fcJDip9PjzhxQYc2 LAvjhcsNyivnWCJEOU8FrbfZz8SnrcQ/iZMnaLKcbKsHFHRvuAimbdquowLVtHqOa4 RCmjt3Olzsw7cgcgo2puzK4BivhFlMkKpMh5FTcR6q5xbekPaGT93pzPYbQcL9m+Jj YSF0+HbqUopvjfqWsvwi8QO52KLaDyoRjowDdkf3B14bewcE+2C9Fe90qkTpzp53Cn 5M+ZN3myCS5L7prGtc6A6gQHCob2wI47ufsYe2PtunhYJAd7aejbx34z2i2tBgUf1h Iv9uXcfjtLolg== Date: Fri, 20 Jun 2025 15:43:02 -0700 From: "H. 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> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable 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