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 88E37C4332F for ; Mon, 12 Dec 2022 22:10:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233056AbiLLWKK (ORCPT ); Mon, 12 Dec 2022 17:10:10 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54490 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233513AbiLLWKF (ORCPT ); Mon, 12 Dec 2022 17:10:05 -0500 Received: from bee.birch.relay.mailchannels.net (bee.birch.relay.mailchannels.net [23.83.209.14]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 76F3BD95 for ; Mon, 12 Dec 2022 14:10:03 -0800 (PST) X-Sender-Id: dreamhost|x-authsender|kjlx@templeofstupid.com Received: from relay.mailchannels.net (localhost [127.0.0.1]) by relay.mailchannels.net (Postfix) with ESMTP id CCD9064114E for ; Mon, 12 Dec 2022 22:10:02 +0000 (UTC) Received: from pdx1-sub0-mail-a304.dreamhost.com (unknown [127.0.0.6]) (Authenticated sender: dreamhost) by relay.mailchannels.net (Postfix) with ESMTPA id 69D11640EE3 for ; Mon, 12 Dec 2022 22:10:02 +0000 (UTC) ARC-Seal: i=1; s=arc-2022; d=mailchannels.net; t=1670883002; a=rsa-sha256; cv=none; b=WDPEGXUUJqWXIX1V9t38/sWkpCLV/zu2q+xLDdYIFxIal4i5o9O+L/MifioiprhY0718AD rk8Xf8sjI9nnik7K28vuAhe0Ru7tJC8rcHm9JbkkxEpztgspBRJqoM+EN6qoxMP/Ytzrcu qZ6UeQkUWlnkWSjqia/WQ68taqac0yEH18EAa/ehOVo8Ad21LDAPR5JcZDl1eb4m5fLupL ISNqw9fOdkUNTBi3YAsBe44shtbEU7WdCDsnkWp3UDoTxOJkrDm7rREtYQQ8AK3pWldbCK BxpuyZdT/hWde+qo7Y9OLxqTnjLXkofOEJ4oj+8jhSPOHK/OWyepFNLLPsKFtw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=mailchannels.net; s=arc-2022; t=1670883002; 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:dkim-signature; bh=pm5eqDMj3rjNgwZzS8R4PcNizlLd7CBAVERWYcW9iw4=; b=ficQm+9VUbqGrpoAthl6W4v++XofTw0CBjXSVT+ow7EPIsFiQt5/BgOEwMVv8aaoen71WV KAsTgsQ0bEKpoKDILPbrvgmTTWOp59Zd58CZtz4NWxW/jNDoVBJ2AagEzKYJpoz8VzSZuu PWCEOV15g6Hda2O1s2uzaYDk19AYMrOwvFbt4pb4GU4QsU6iCKOfhzRsd2F0HA0NMCoPGb Ks0k9Ve3ibMHzjZVZY4nVakYFMQLi+V6rkifrtbSDoAN79r9oSwVqK4+/fGgchTsjVGcci BMLe6ITP5xhEREEeQVEUa/bzFov2JT1VYketvHZtiIiApe6EVLNxWgxDlUuIFg== ARC-Authentication-Results: i=1; rspamd-d48c5ddb-rh68f; auth=pass smtp.auth=dreamhost smtp.mailfrom=kjlx@templeofstupid.com X-Sender-Id: dreamhost|x-authsender|kjlx@templeofstupid.com X-MC-Relay: Neutral X-MailChannels-SenderId: dreamhost|x-authsender|kjlx@templeofstupid.com X-MailChannels-Auth-Id: dreamhost X-Eyes-Harmony: 1ea9aabb66ae881a_1670883002660_3739976796 X-MC-Loop-Signature: 1670883002660:1453000785 X-MC-Ingress-Time: 1670883002660 Received: from pdx1-sub0-mail-a304.dreamhost.com (pop.dreamhost.com [64.90.62.162]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384) by 100.126.30.15 (trex/6.7.1); Mon, 12 Dec 2022 22:10:02 +0000 Received: from kmjvbox (c-73-70-108-208.hsd1.ca.comcast.net [73.70.108.208]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: kjlx@templeofstupid.com) by pdx1-sub0-mail-a304.dreamhost.com (Postfix) with ESMTPSA id 4NWG5P5y36zh2 for ; Mon, 12 Dec 2022 14:10:01 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=templeofstupid.com; s=dreamhost; t=1670883001; bh=pm5eqDMj3rjNgwZzS8R4PcNizlLd7CBAVERWYcW9iw4=; h=Date:From:To:Cc:Subject:Content-Type; b=f9hSBodhCnCMpYIiSsG8QLdPAzLYTZ5bzy4zI0VIMnlbZDqxmnP5CgZslJn9VF2St t0hhglW3mSrJgJLRCw9L7LX0Z5YSLRYQVDEN4mZZ5Kd9Ht4PFuZv3x+XURi/eONFKt lKcybtBYxxFSmWg+nH1cieN9Xrhs8usIGK78YYzM= Received: from johansen (uid 1000) (envelope-from kjlx@templeofstupid.com) id e0085 by kmjvbox (DragonFly Mail Agent v0.12); Mon, 12 Dec 2022 14:09:59 -0800 Date: Mon, 12 Dec 2022 14:09:59 -0800 From: Krister Johansen To: Boris Ostrovsky Cc: Krister Johansen , Juergen Gross , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, Marcelo Tosatti , Anthony Liguori , David Reaver , Brendan Gregg Subject: Re: [PATCH linux-next v2] x86/xen/time: prefer tsc as clocksource when it is invariant Message-ID: <20221212220959.GB1935@templeofstupid.com> References: <20221208163650.GA3225@templeofstupid.com> <1e6c1b08-d573-fba9-61fd-d40a74427d46@oracle.com> <20221212155730.GA1973@templeofstupid.com> <20221212160524.GB1973@templeofstupid.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 12, 2022 at 01:48:24PM -0500, Boris Ostrovsky wrote: > > On 12/12/22 11:05 AM, Krister Johansen wrote: > > > > diff --git a/arch/x86/include/asm/xen/cpuid.h b/arch/x86/include/asm/xen/cpuid.h > > index 6daa9b0c8d11..d9d7432481e9 100644 > > --- a/arch/x86/include/asm/xen/cpuid.h > > +++ b/arch/x86/include/asm/xen/cpuid.h > > @@ -88,6 +88,12 @@ > > * EDX: shift amount for tsc->ns conversion > > * Sub-leaf 2: EAX: host tsc frequency in kHz > > */ > > +#define XEN_CPUID_TSC_EMULATED (1u << 0) > > +#define XEN_CPUID_HOST_TSC_RELIABLE (1u << 1) > > +#define XEN_CPUID_RDTSCP_INSTR_AVAIL (1u << 2) > > +#define XEN_CPUID_TSC_MODE_DEFAULT (0) > > +#define XEN_CPUID_TSC_MODE_EMULATE (1u) > > +#define XEN_CPUID_TSC_MODE_NOEMULATE (2u) > > This file is a copy of Xen public interface so this change should go to Xen first. Ok, should I split this into a separate patch on the linux side too? > > +static int __init xen_tsc_safe_clocksource(void) > > +{ > > + u32 eax, ebx, ecx, edx; > > + > > + if (!(xen_hvm_domain() || xen_pvh_domain())) > > + return 0; > > + > > + if (!(boot_cpu_has(X86_FEATURE_CONSTANT_TSC))) > > + return 0; > > + > > + if (!(boot_cpu_has(X86_FEATURE_NONSTOP_TSC))) > > + return 0; > > + > > + if (check_tsc_unstable()) > > + return 0; > > + > > + cpuid(xen_cpuid_base() + 3, &eax, &ebx, &ecx, &edx); > > + > > + if (eax & XEN_CPUID_TSC_EMULATED) > > + return 0; > > + > > + if (ebx != XEN_CPUID_TSC_MODE_NOEMULATE) > > + return 0; > > Why is the last test needed? I was under the impression that if the mode was 0 (default) it would be possible for the tsc to become emulated in the future, perhaps after a migration. The presence of the tsc_mode noemulate meant that we could count on the falseneess of the XEN_CPUID_TSC_EMULATED check remaining constant. -K