From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=90.155.92.199 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793617331; b=D+X4/UQyzrxqR7MtmakZU8z5Qqwkt7ieEDQ8jvqo4UG+ZoRCQrhamT8fE9yteLZUMRFE LKa23NsXk+j9gHl6DR0Xe1wqhydw2HzbkcOrZGfI0tV3iBzanScIr2S3F8z55rUO2K8Ck aX/rlPMey+HFmhNZXv3ajL8PLwBYyDpOkBSGgF5/RfpcgRUiWgw5NY7EyLpgGN9trqZ2l vhqwxRQCsJdltIBS9R29dPcoW09QQBLxPMSV83I+wSJy253qeYKzmE4wTi0EaEKQS1fVt iIjYqvvr5AQglhqTqwSA2JIUU59ctZJEdZv6ezRHbpOjPG9YEqUzBCzWUSXmy/PbUaw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793617331; h=DMARC-Filter:DKIM-Signature:Received:Received:Date:From:To:Cc: Subject:Message-ID:References:MIME-Version:Content-Type: Content-Disposition:In-Reply-To; bh=4U44tyM9rIQqvE/aal0rqvdOLJnVYtfYiLLnwvN3EA4=; b=k9dRgKqXJ50yb0jmf/IMb4QiuQn1BUSW3dQsvYWov2uuOEeegbe2DjbIdPBlZvtlrGpC bD5cuvz75Lc4+6Bn87Sgt46CMqn8JxcOrmjK/xKI/1feG2AbmDPF8ZFxcgqc8u3q5IDYV TfM4BzW9o0S3od8tjMOtfqeYleEAV8rXFoTi9aa7KYigr9CuayyLOMwVACkRig6CAGoxb s9XTAY6xN5c49WjyuRvuQthojydYUOMniNtNBf0U+n9uAGSwiNseW1/YfAHWdnwE4sPTi 47mzmjKVnlomq/ltDLkFxvHC+ck64DkWGixMkPSDf/ZrYi9y4AUk62yHzK76J13NOnA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256 header.s=desiato.20200630 header.b=nbM1qdyL; arc=none smtp.remote-ip=90.155.92.199 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0E661606A324; Mon, 2 Nov 2026 11:02:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 0E661606A324 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256 header.s=desiato.20200630 header.b=nbM1qdyL DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=4U44tyM9rIQqvE/aal0rqvdOLJnVYtfYiLLnwvN3EA4=; b=nbM1qdyLyua88iak+CnnYnpVBy A1BLNFiUQECLsqB1mBS05ytv3y/Hu3eNb6xt8YECvyZ1+/1GinHSbprhZsH/L5iLTFJVfhRzqoUM7 RNHg53XBizU0Km6DuMJaaP5e03/BbLnaGaY5iwqFEeGab7MWJMfl3fW3Jq/3AOCLquw2OesEQKTma vu2+J/uV/G9OaJcBjCd3jCJ8lBR2SzYR++lxpmVBJQksabU08H4MLYSJ6x3uHu6A0n9jGcRi61miM IImDficcUenSX91Xc9UVX8k/HGPXW8wHeCf97lockJPE54fn/NFJG4d6Ryo+uY+0qa3TuiSS5xWJ+ IqDtJ9qw==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.100.1 #2 (Red Hat Linux)) id 1xNpnb-00000002PG9-3Imb; Mon, 02 Nov 2026 11:02:00 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 93D073002ED; Mon, 02 Nov 2026 12:01:58 +0100 (CET) Date: Mon, 2 Nov 2026 12:01:58 +0100 From: Peter Zijlstra To: Adrian Hunter Cc: Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , James Clark , Thomas Gleixner , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , "Rafael J. Wysocki" , Pavel Machek , Greg Kroah-Hartman , Danilo Krummrich , Johan Hovold , Sebastian Andrzej Siewior , Mathieu Desnoyers , Jiayuan Chen , "Steven Rostedt (Google)" , "Vineeth Pillai (Google)" , Frederic Weisbecker , Andi Kleen , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, driver-core@lists.linux.dev Subject: Re: [PATCH 3/6] perf/x86/intel/pt: Stop tracing at syscore shutdown Message-ID: <20261102110158.GW1779021@noisy.programming.kicks-ass.net> References: <20261102074039.26983-1-adrian.hunter@intel.com> <20261102074039.26983-4-adrian.hunter@intel.com> <20261102100451.GT1779021@noisy.programming.kicks-ass.net> <8cd3d3f3-c866-4ed3-a41f-a4210e2d73c2@intel.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8cd3d3f3-c866-4ed3-a41f-a4210e2d73c2@intel.com> On Mon, Nov 02, 2026 at 12:23:57PM +0200, Adrian Hunter wrote: > On 02/11/2026 12:04, Peter Zijlstra wrote: > > On Mon, Nov 02, 2026 at 09:40:36AM +0200, Adrian Hunter wrote: > >> +static void pt_shutdown_cpu(void *info) > >> +{ > >> + u64 ctl; > >> + > >> + /* > >> + * After VMXON on CPUs without PT support in VMX operation, > >> + * TraceEn is already clear and RTIT_CTL must not be written. > >> + */ > >> + rdmsrq(MSR_IA32_RTIT_CTL, ctl); > >> + if (ctl & RTIT_CTL_TRACEEN) > >> + wrmsrq(MSR_IA32_RTIT_CTL, ctl & ~RTIT_CTL_TRACEEN); > >> +} > > > > Why not unconditionally do: wrmsrq(MSR_IA32_RTIT_CTL, 0), at this point? > > Writing 0 instead of ctl & ~RTIT_CTL_TRACEEN would be fine, but the > condition is needed. The comment tries to explain. > > The first processor to support Intel PT (BDW) will #GP if a write is > made to RTIT_CTL while VMX is on. Since VMXON clears TRACEEN, > if TRACEEN is set, then the write is safe. I hate computers...