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 X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 902ACC433B4 for ; Thu, 20 May 2021 21:13:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5FF06610CB for ; Thu, 20 May 2021 21:13:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229971AbhETVOp (ORCPT ); Thu, 20 May 2021 17:14:45 -0400 Received: from mga03.intel.com ([134.134.136.65]:53990 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229807AbhETVOo (ORCPT ); Thu, 20 May 2021 17:14:44 -0400 IronPort-SDR: xU3QX6bKDUwIlCOjcuhvItrivyUa2nlFmCWJej3JlK9iKs2Y3fu5jjjuid5KEY9yVPjRvoCP7k V9ubvLQjJBZQ== X-IronPort-AV: E=McAfee;i="6200,9189,9990"; a="201395050" X-IronPort-AV: E=Sophos;i="5.82,313,1613462400"; d="scan'208";a="201395050" Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 May 2021 14:13:20 -0700 IronPort-SDR: 8zrSE+p1g3TFsi2gQdEcdoC0bLVukRiIA8LGfjCy+e39vOf0/Gt5Ln0fMavoke/DMyUFXV7yWH Mhaf/hWurZ+g== X-IronPort-AV: E=Sophos;i="5.82,313,1613462400"; d="scan'208";a="543769119" Received: from blydon-mobl.amr.corp.intel.com (HELO [10.209.0.109]) ([10.209.0.109]) by fmsmga001-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 May 2021 14:13:18 -0700 Subject: Re: Candidate Linux ABI for Intel AMX and hypothetical new related features To: Thomas Gleixner , Len Brown Cc: Borislav Petkov , Willy Tarreau , Andy Lutomirski , Florian Weimer , "Bae, Chang Seok" , X86 ML , LKML , Linux API , "libc-alpha@sourceware.org" , Rich Felker , Kyle Huey , Keno Fischer , Arjan van de Ven References: <20210415044258.GA6318@zn.tnic> <20210415052938.GA2325@1wt.eu> <20210415054713.GB6318@zn.tnic> <20210419141454.GE9093@zn.tnic> <20210419191539.GH9093@zn.tnic> <20210419215809.GJ9093@zn.tnic> <874kf11yoz.ffs@nanos.tec.linutronix.de> <87k0ntazyn.ffs@nanos.tec.linutronix.de> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <87k0ntazyn.ffs@nanos.tec.linutronix.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On 5/20/21 1:54 PM, Thomas Gleixner wrote: >> Regarding error return for allocation failures. >> >> I'm not familiar with the use-case where vmalloc would be likely to fail today, >> and I'd be interested if anybody can detail that use-case. > It does not matter whether it's likely or not. Unlikely simply does not > exist at cloud-scale. Len, I may have led you astray in some of our discussions on this topic. Here are the cold hard facts: * vmalloc() can fail (the memory.kmem cgroup limit is probably the most likely place to be exposed to this) * vmalloc() failure in a fault (like #NM) will result in SIGSEGV * vmalloc() failure in a syscall can be handled with -ENOMEM In some of our discussions, I told you that reasonably-sized vmalloc()s don't practically fail and that we shouldn't be concerned with failure for our vmalloc()-in-#NM use-case. In other words, I'm OK with crashing apps at the point that vmalloc() is failing. However, Thomas was pretty clear that he's not OK with that. To paraphrase: if we can avoid expanding the scope of where memory allocation failures result in SIGSEGV, we should do it. While I don't *entirely* agree that it's worth it, I can respect Thomas's opinion here. It leads me in the direction of wanting to drive dynamic xstate vmalloc()s from an explicit syscall ABI. My apologies if I sent the AMX support on an unproductive tangent here.