From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH] perf/x86/intel/pt: Don't die on VMXON
Date: Wed, 6 Apr 2016 13:52:15 +0200
Message-ID: <20160406115215.GK2906@worktop>
References: <1459527854-5899-1-git-send-email-alexander.shishkin@linux.intel.com>
 <20160406085227.GO3448@twins.programming.kicks-ass.net>
 <87vb3v56x2.fsf@ashishki-desk.ger.corp.intel.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Gleb Natapov <gleb@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>, x86@kernel.org,
	kvm@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
	linux-kernel@vger.kernel.org, tglx@linutronix.de, hpa@zytor.com,
	Arnaldo Carvalho de Melo <acme@infradead.org>,
	Borislav Petkov <bp@alien8.de>
To: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from bombadil.infradead.org ([198.137.202.9]:45365 "EHLO
	bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751660AbcDFLw3 (ORCPT <rfc822;kvm@vger.kernel.org>);
	Wed, 6 Apr 2016 07:52:29 -0400
Content-Disposition: inline
In-Reply-To: <87vb3v56x2.fsf@ashishki-desk.ger.corp.intel.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

On Wed, Apr 06, 2016 at 02:10:49PM +0300, Alexander Shishkin wrote:
> >> +	/* may be already stopped by a PMI*/
> >> +	if (!(ctl & RTIT_CTL_TRACEEN))
> >> +		return;
> >> +
> >> +	ctl ^= RTIT_CTL_TRACEEN;
> >
> > Would that not be much less confusing when written like |= ?
> 
> This one's actually clearing TraceEn, see the if-not-set-leave in front
> of it, but that just goes to prove your point I guess. :)

Hehe, indeed. So much for pretending to be awake :-)


> How about this then:

Looks good, however:

> +	if (test_cpu_cap(&boot_cpu_data, X86_FEATURE_VMX)) {

Borislav tells me this ought to be boot_cpu_has(X86_FEATURE_VMX)

> +		/* Intel SDM, 36.5 "Tracing post-VMXON" */
> +		rdmsrl(MSR_IA32_VMX_MISC, reg);
> +		if (reg & BIT(14))
> +			pt_pmu.vmx = true;
> +	}