Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752681AbZKAXg6 (ORCPT ); Sun, 1 Nov 2009 18:36:58 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752274AbZKAXg5 (ORCPT ); Sun, 1 Nov 2009 18:36:57 -0500 Received: from mail-ew0-f228.google.com ([209.85.219.228]:43940 "EHLO mail-ew0-f228.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751059AbZKAXg4 (ORCPT ); Sun, 1 Nov 2009 18:36:56 -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=xyGsemp3XCqMi8X/rGdBX2g5Fza/clhKMKmJtYjMj6gupd8vZ4vOi8/gOaNjeHEZ3K DdbMqQmeyqxROTn6Se0P//AKFUSErq888QWhPiYG/hvo2ZFt/4iB2fT2HXthSiLjC0qs T+WLuPbNUDPuvv/bAM9TbeiTXNyDmUxn2nV+o= Date: Mon, 2 Nov 2009 00:37:01 +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: <20091101233659.GE5263@nowhere> References: <4AE55B1B.2030006@web.de> <1257109753-6464-5-git-send-email-fweisbec@gmail.com> <4AEE06FF.9080807@web.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4AEE06FF.9080807@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: 1897 Lines: 44 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. 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. -- 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/