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[23.128.96.18]) by mx.google.com with ESMTP id j11si14124047pff.168.2021.05.03.11.08.05; Mon, 03 May 2021 11:08:18 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=intel.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233981AbhECNoy (ORCPT + 99 others); Mon, 3 May 2021 09:44:54 -0400 Received: from mga07.intel.com ([134.134.136.100]:16990 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233159AbhECNow (ORCPT ); Mon, 3 May 2021 09:44:52 -0400 IronPort-SDR: igZMK4p0+VSErBnlZSJBgaXC2WrNd4qwa/Za1fFjLn6+f38ZxB05vx6rQTGLH2hfKNIYFoTH+4 9iRplGrAjD3g== X-IronPort-AV: E=McAfee;i="6200,9189,9973"; a="261693257" X-IronPort-AV: E=Sophos;i="5.82,270,1613462400"; d="scan'208";a="261693257" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 May 2021 06:43:58 -0700 IronPort-SDR: 1Q7MgqpsbVcrOOY5O4IJnH4Dx1Wk8xsoYTEgORSggA5q2Lcazr4uHA4+SikEGv8l5DFj4lavzZ H8B28SkzzRRA== X-IronPort-AV: E=Sophos;i="5.82,270,1613462400"; d="scan'208";a="432747792" Received: from tbroiles-mobl.amr.corp.intel.com (HELO [10.209.47.222]) ([10.209.47.222]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 May 2021 06:43:56 -0700 Subject: Re: Candidate Linux ABI for Intel AMX and hypothetical new related features To: Florian Weimer , Len Brown Cc: Borislav Petkov , Willy Tarreau , Andy Lutomirski , "Bae, Chang Seok" , X86 ML , LKML , linux-abi@vger.kernel.org, "libc-alpha@sourceware.org" , Rich Felker , Kyle Huey , Keno Fischer 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> <87bl9s8kfb.fsf@oldenburg.str.redhat.com> 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: <87bl9s8kfb.fsf@oldenburg.str.redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/2/21 10:18 PM, Florian Weimer wrote: >> 5. If the feature is enabled in XCR0, the user happily uses it. >> >> For AMX, Linux implements "transparent first use" >> so that it doesn't have to allocate 8KB context switch >> buffers for tasks that don't actually use AMX. >> It does this by arming XFD for all tasks, and taking a #NM >> to allocate a context switch buffer only for those tasks >> that actually execute AMX instructions. > What happens if the kernel cannot allocate that additional context > switch buffer? Well, it's vmalloc()'d and currently smaller that the kernel stack, which is also vmalloc()'d. While it can theoretically fail, if it happens you have bigger problems on your hands.