From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1757577Ab0DOI5y (ORCPT <rfc822;w@1wt.eu>);
	Thu, 15 Apr 2010 04:57:54 -0400
Received: from mga05.intel.com ([192.55.52.89]:42126 "EHLO
	fmsmga101.fm.intel.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org
	with ESMTP id S1757449Ab0DOI5w (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 15 Apr 2010 04:57:52 -0400
X-ExtLoop1: 1
X-IronPort-AV: E=Sophos;i="4.52,211,1270450800"; 
   d="scan'208";a="558173466"
Subject: Re: [PATCH V3] perf & kvm: Enhance perf to collect KVM guest os
 statistics from host side
From: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
To: Avi Kivity <avi@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Sheng Yang <sheng@linux.intel.com>, linux-kernel@vger.kernel.org,
       kvm@vger.kernel.org, Marcelo Tosatti <mtosatti@redhat.com>,
       oerg Roedel <joro@8bytes.org>, Jes Sorensen <Jes.Sorensen@redhat.com>,
       Gleb Natapov <gleb@redhat.com>, Zachary Amsden <zamsden@redhat.com>,
       zhiteng.huang@intel.com, tim.c.chen@intel.com,
       Arnaldo Carvalho de Melo <acme@infradead.org>
In-Reply-To: <4BC6C8CD.1020801@redhat.com>
References: <1902387910.2078.435.camel@ymzhang.sh.intel.com>
	 <4BC588CF.5010507@redhat.com>
	 <1902445479.2078.458.camel@ymzhang.sh.intel.com>
	 <4BC6C8CD.1020801@redhat.com>
Content-Type: text/plain; charset="ISO-8859-1"
Date: Mon, 15 Apr 2030 16:57:38 +0800
Message-Id: <1902473858.2078.481.camel@ymzhang.sh.intel.com>
Mime-Version: 1.0
X-Mailer: Evolution 2.28.0 (2.28.0-2.fc12) 
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, 2010-04-15 at 11:05 +0300, Avi Kivity wrote:
> On 04/15/2030 04:04 AM, Zhang, Yanmin wrote:
> >
> >> An even more accurate way to determine this is to check whether the
> >> interrupt frame points back at the 'int $2' instruction.  However we
> >> plan to switch to a self-IPI method to inject the NMI, and I'm not sure
> >> wether APIC NMIs are accepted on an instruction boundary or whether
> >> there's some latency involved.
> >>      
> > Yes. But the frame pointer checking seems a little complicated.
> >    
> 
> An even bigger disadvantage is that it won't work with Sheng's patch, 
> self-NMIs are not synchronous.
> 
> >>>    	trace_kvm_entry(vcpu->vcpu_id);
> >>> +
> >>> +	percpu_write(current_vcpu, vcpu);
> >>>    	kvm_x86_ops->run(vcpu);
> >>> +	percpu_write(current_vcpu, NULL);
> >>>
> >>>        
> >> If you move this around the 'int $2' instructions you will close the
> >> race, as a stray NMI won't catch us updating the rip cache.  But that
> >> depends on whether self-IPI is accepted on the next instruction or not.
> >>      
> > Right. The kernel part has dependency on the self-IPI implementation.
> > I will move above percpu_write(current_vcpu, vcpu) (or a new wrapper function)
> > just around 'int $2'.
> >
> >    
> 
> Or create a new function to inject the interrupt in x86.c.  That will 
> reduce duplication between svm.c and vmx.c.
I checked svm.c and it seems svm.c doesn't trigger a NMI to host if the NMI
happens in guest os. In addition, svm_complete_interrupts is called after
interrupt is enabled.