Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755148AbZKBNEh (ORCPT ); Mon, 2 Nov 2009 08:04:37 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755084AbZKBNEg (ORCPT ); Mon, 2 Nov 2009 08:04:36 -0500 Received: from mail-bw0-f227.google.com ([209.85.218.227]:38797 "EHLO mail-bw0-f227.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755080AbZKBNEf (ORCPT ); Mon, 2 Nov 2009 08:04:35 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=lbqlNVPJvOl98nxQYltzsfS01534vC1zZZcLEWXQGLGrl9PY7GTSkDMPmEbiTqGjNi 202poL44A1JX3rrrIjn5PxGyDLUfh08gVfDwGzTmG7P1k/5JlJHX0PDvoiRGdtlcJny5 U01lLJoHO7qw6nR2bjMDrG3fLQjLoPLtapLWk= Date: Mon, 2 Nov 2009 14:04:40 +0100 From: Frederic Weisbecker To: Jan Kiszka Cc: Ingo Molnar , LKML , Prasad , Alan Stern , Peter Zijlstra , Arnaldo Carvalho de Melo , Steven Rostedt , Jiri Slaby , Li Zefan , Avi Kivity , Paul Mackerras , Mike Galbraith , Masami Hiramatsu , Paul Mundt Subject: Re: [PATCH 4/6] hw-breakpoints: Rewrite the hw-breakpoints layer on top of perf events Message-ID: <20091102130434.GC4878@nowhere> References: <4AE55B1B.2030006@web.de> <1257109753-6464-5-git-send-email-fweisbec@gmail.com> <4AEE06FF.9080807@web.de> <20091101233659.GE5263@nowhere> <4AEE8E34.8080105@web.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4AEE8E34.8080105@web.de> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2787 Lines: 66 On Mon, Nov 02, 2009 at 08:45:56AM +0100, Jan Kiszka wrote: > Frederic Weisbecker wrote: > > On Sun, Nov 01, 2009 at 11:09:03PM +0100, Jan Kiszka wrote: > >>> @@ -3643,14 +3644,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run) > >>> trace_kvm_entry(vcpu->vcpu_id); > >>> kvm_x86_ops->run(vcpu, kvm_run); > >>> > >>> - if (unlikely(vcpu->arch.switch_db_regs || test_thread_flag(TIF_DEBUG))) { > >>> - set_debugreg(current->thread.debugreg[0], 0); > >>> - set_debugreg(current->thread.debugreg[1], 1); > >>> - set_debugreg(current->thread.debugreg[2], 2); > >>> - set_debugreg(current->thread.debugreg[3], 3); > >>> - set_debugreg(current->thread.debugreg6, 6); > >>> - set_debugreg(current->thread.debugreg7, 7); > >>> - } > >>> + if (unlikely(vcpu->arch.switch_db_regs || test_thread_flag(TIF_DEBUG))) > >>> + hw_breakpoint_restore(); > >> TIF_DEBUG is only set on active ptrace hw-breakpoints, thus we miss > >> other types here, right? (Note: arch.switch_db_regs is guest-related, > >> thus does not help in this regard.) > >> > >> Jan > >> > > > > > > About this. vcpu->arch.switch_db_regs is guest related but it looks > > like the only thing I need to check. > > > > I'm not sure when it is activated. Is it always done once the guest > > changes its debug registers? I suspect there is a corner case. > > It's set when we had to write to some debugreg[0..4], either for use by > the guest itself or for debugging it from the host. It used to be the > only condition for switching on exit as we saved the registers on entry > (under the same condition). This was reworked recently to avoid the > entry saving. > > > > > Because since I can't anymore assume TIF_DEBUG covers every > > breakpoints uses, it means I'll need to maintain a refcount of > > breakpoints in use. > > Well, I have one already, but it is splitted into several refcounts > > (per task events, per cpu, non-pinned, etc...). And since > > vcpu_enter_guest() is a fast path, I'll need to maintain another global > > per cpu one, without lock or further operations to know if we need > > to save the debug registers, just a simple check. > > > > I'm not 100% sure right now if we still need "switch_db_reg" in case we > have a reliable indicator that the host requires properly set registers. > ATM I would dare to say, we don't, but I need to think about this again. > > Jan > Ok. I'm going to just check if the host has active breakpoints pending and if so, I'll restore them while exiting the guest. Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/