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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 C1AD7C433ED for ; Mon, 17 May 2021 10:18:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A50EB611CA for ; Mon, 17 May 2021 10:18:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236373AbhEQKTb (ORCPT ); Mon, 17 May 2021 06:19:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40230 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230248AbhEQKT3 (ORCPT ); Mon, 17 May 2021 06:19:29 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DAF60C061573; Mon, 17 May 2021 03:18:11 -0700 (PDT) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1621246690; 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=+zz3NPs+wt6StysgikNkYNgGUFeAfLSA7zXm/ZKg27k=; b=DXHJbrfh4uoRQpWx9h9zfiHD+Q5JOAd143oFu1shjaH85Ky7o+V2cari7L/ZvBUb1hLYO8 5wSieOg2XbhI/alz4CI6023AiDJs6hVTk1cukX8VuDXNExOc9KX2CtkJcAwqec9W8j+sJs DnQXwtEdD3dunRZ38Pl4rmKiCWoZdwWFWSEExbHKxmGjM3ZISfWS0J+dsO0pD8FvXg1a2T kUFf8RqIrMEeXqPl+CR2LS6XhbT6WaYoQfT5EOn0mwS+3PapV0t/kEQmEDHDpKablHwjYy dz7DPdTEbKJ3GzwmGMr4PU/N6/jixx70Okrj+Ju7DOT82ZmNCrOUCEnsPnYfNA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1621246690; 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=+zz3NPs+wt6StysgikNkYNgGUFeAfLSA7zXm/ZKg27k=; b=mghAS2q0UHTE2Lmbb//Xqw/ACQntH5qxeu2VotZwfZuEumALz9iuphq2aT5JdwvI9gFMi6 04sD7+l4zKemAkBA== To: Florian Weimer Cc: Len Brown , Borislav Petkov , Willy Tarreau , Andy Lutomirski , "Bae\, Chang Seok" , Dave Hansen , X86 ML , LKML , linux-api@vger.kernel.org, "libc-alpha\@sourceware.org" , Rich Felker , Kyle Huey , Keno Fischer , Arjan van de Ven Subject: Re: Candidate Linux ABI for Intel AMX and hypothetical new related features In-Reply-To: <87pmxpk7jo.fsf@oldenburg.str.redhat.com> 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> <87pmxpk7jo.fsf@oldenburg.str.redhat.com> Date: Mon, 17 May 2021 12:18:10 +0200 Message-ID: <87y2cdzmsd.ffs@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 17 2021 at 11:56, Florian Weimer wrote: > * Thomas Gleixner: > >> Having a proper interface (syscall, prctl) which user space can use to >> ask for permission and allocation of the necessary buffer(s) is clearly >> avoiding the downsides and provides the necessary mechanisms for proper >> control and failure handling. >> >> It's not the end of the world if something which wants to utilize this >> has do issue a syscall during detection. It does not matter whether >> that's a library or just the application code itself. >> >> That's a one off operation and every involved entity can cache the >> result in TLS. > > I'm not sure if it's a good idea to have each AMX consumer to set up its > own TLS cache. How expensive is checking XCR0 via XGETBV instead on the > AMX path? Then AMX can be enabled on the thread via a system call. Right, did not think about that. > It also allows disabling of AMX. That needs reference counting, but yes it's possible. > It would also need an AT_HWCAP2 feature flag telling user space that AMX > support is available after that system call (switching on AMX to check > whether AMX paths should enabled later seems potentially wasteful if the > AMX paths are never taken after all). Either that or just have: prctl(PR_QUERY_XSTATE_FEATURES,.... prctl(PR_ENABLE_XSTATE_FEATURES,.... prctl(PR_DISABLE_XSTATE_FEATURES,.... Thanks, tglx