From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: [PATCH] trace "exit to userspace" event Date: Sun, 10 Oct 2010 17:46:25 +0200 Message-ID: <20101010154625.GR2397@redhat.com> References: <20101005131432.GO11145@redhat.com> <20101007161839.GA31784@amt.cnet> <20101007175655.GG2397@redhat.com> <20101008004917.GA11600@amt.cnet> <20101008164447.GC393@redhat.com> <4CB17D39.7020007@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Marcelo Tosatti , kvm@vger.kernel.org To: Avi Kivity Return-path: Received: from mx1.redhat.com ([209.132.183.28]:49560 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753449Ab0JJPq0 (ORCPT ); Sun, 10 Oct 2010 11:46:26 -0400 Received: from int-mx08.intmail.prod.int.phx2.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.21]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id o9AFkQox011459 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Sun, 10 Oct 2010 11:46:26 -0400 Content-Disposition: inline In-Reply-To: <4CB17D39.7020007@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Sun, Oct 10, 2010 at 10:45:45AM +0200, Avi Kivity wrote: > On 10/08/2010 06:44 PM, Gleb Natapov wrote: > >On Thu, Oct 07, 2010 at 09:49:17PM -0300, Marcelo Tosatti wrote: > >> On Thu, Oct 07, 2010 at 07:56:55PM +0200, Gleb Natapov wrote: > >> > > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > >> > > > index b8499f5..8800713 100644 > >> > > > --- a/virt/kvm/kvm_main.c > >> > > > +++ b/virt/kvm/kvm_main.c > >> > > > @@ -1458,6 +1458,8 @@ static long kvm_vcpu_ioctl(struct file *filp, > >> > > > if (arg) > >> > > > goto out; > >> > > > r = kvm_arch_vcpu_ioctl_run(vcpu, vcpu->run); > >> > > > + if (r>= 0) > >> > > > + trace_kvm_userspace_exit(vcpu->run->exit_reason); > >> > > > break; > >> > > > case KVM_GET_REGS: { > >> > > > struct kvm_regs *kvm_regs; > >> > > > -- > >> > > > Gleb. > >> > > > >> > > Exit codes are also valid for r == -EINTR and -EAGAIN cases, eg > >> > > EXIT_INTR. Better print it out for all cases, and let the reader > >> > > decide whether exit_reason is valid. > >> > Are they? I see that userspace does not look into run->exit_reason in > >> > case of -EINTR and -EAGAIN. > >> > >> Not userspace, but for a human reader. Otherwise the trace information > >> is incomplete and confusing. > >But if we will always call trace_kvm_userspace_exit() here trace > >information will show erroneous info since on any error but -EINTR > >exit_reason contains stale info. What about changing r>= 0 to r>= 0 || > >r == -EINTR. > > We should log both errno and exit_reason. If we want to be clever, > we can display strerror(errno) if it's nonzero, and exit_reason > otherwise (easy to do in a trace-cmd plugin). > For starters we should remove KVM_EXIT_INTR exit reason. Looking into qemu-kvm history it was never used and there is at least one code path that returns -EINTR and does not set KVM_EXIT_INTR, so exit_reason field contains stale info on exit. -- Gleb.