From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6AC57C433EF for ; Thu, 12 May 2022 19:31:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1358046AbiELTba (ORCPT ); Thu, 12 May 2022 15:31:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57084 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1358038AbiELTb0 (ORCPT ); Thu, 12 May 2022 15:31:26 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1BBCB3BBC8 for ; Thu, 12 May 2022 12:31:24 -0700 (PDT) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1652383882; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=ZGtrQksjQfamBywCmnK7pPuFj4WwCjQmxlrTTj3S/6I=; b=1T8MYAwPo2BEm/6WmMHLKCbQY3p/N6rOZLdz3iI4vaCMn8SA7CLKFECG9eIE+7gOpqhtq/ CaILNXJySrPfWNjAViBxh5vkMssMmhwsFL3Kp9fXPhwG3f/KBLUHBL2Empa6yJ5AwS5PUf Wz1wU8NADjeRlzrsLDpjAM7ZQGYwBdj8knj/SZmnjtdZb+JhTtKpKLKxENV1tTySs0iQAC uyCBRZg1Jkga0NA5a7AnSlYbAYyuaELHKoFFKKgNFk94XvqlhJKPSEvD8ck/qS9kcxdwE1 ADCkse3eItboihLHZwQjgBx2NnbvSkomFr7RB54CQCX8Q2X6hzNwnuC6FHJjEg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1652383882; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=ZGtrQksjQfamBywCmnK7pPuFj4WwCjQmxlrTTj3S/6I=; b=ZBiQRbX7ElsW/WoC766JtZsjlIY4BrgDJBq/ChyizEXD64Qh1JWjnOli+d7aHN2ZxjqRYq FfbBeDw3SZHDZ0Aw== To: "Kirill A. Shutemov" , Dmitry Vyukov Cc: Peter Zijlstra , Dave Hansen , Andy Lutomirski , x86@kernel.org, Alexander Potapenko , "H . J . Lu" , Andi Kleen , Rick Edgecombe , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dmitry Vyukov Subject: Re: [RFCv2 00/10] Linear Address Masking enabling In-Reply-To: <20220512165612.gizedzgtpzbi7jbl@black.fi.intel.com> References: <20220511022751.65540-1-kirill.shutemov@linux.intel.com> <20220511064943.GR76023@worktop.programming.kicks-ass.net> <87pmkivjst.ffs@tglx> <20220512165612.gizedzgtpzbi7jbl@black.fi.intel.com> Date: Thu, 12 May 2022 21:31:22 +0200 Message-ID: <878rr6v985.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 12 2022 at 19:56, Kirill A. Shutemov wrote: > On Thu, May 12, 2022 at 05:42:58PM +0200, Thomas Gleixner wrote: >> On Wed, May 11 2022 at 08:49, Peter Zijlstra wrote: >> > On Wed, May 11, 2022 at 05:27:40AM +0300, Kirill A. Shutemov wrote: >> > So aren't we creating a problem with LAM_U48 where programs relying on >> > it are of limited sustainability? >> > >> > Any such program simply *cannot* run on 5 level pagetables. Why do we >> > want to do this? >> >> More bits are better :) >> >> Seriously, I agree that restricting it to LAM57, which gives us 6 bits, >> makes a lot of sense _and_ makes the whole thing way simpler. >> >> So supporting both needs a truly good justification and a real world use >> case. > > I asked the question before[1]. Basically, more bits more better: > > For HWASAN #bits == detection probability. > For MarkUS #bits == exponential cost reduction What is MarkUS? It's not really helpful to provide acronyms which are not decodable. > I would really like to have only LAM_U57, but IIUC 6 bits is not always > enough. > > Dmitry, could you elaborate? > > [1] https://mobile.twitter.com/dvyukov/status/1342019823400837120 I don't know whether he reacts on posting a link to his twitter account. I've CC'ed him now. Maybe that works better. Thanks, tglx