From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758234Ab2C1Oe5 (ORCPT ); Wed, 28 Mar 2012 10:34:57 -0400 Received: from acsinet15.oracle.com ([141.146.126.227]:32292 "EHLO acsinet15.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752127Ab2C1Oez (ORCPT ); Wed, 28 Mar 2012 10:34:55 -0400 Date: Wed, 28 Mar 2012 10:29:28 -0400 From: Konrad Rzeszutek Wilk To: "Liu, Jinsong" Cc: Konrad Rzeszutek Wilk , "keir.xen@gmail.com" , "xen-devel@lists.xensource.com" , Kernel development list , Jan Beulich Subject: Re: [Xen-devel] [PATCH 1/3] PAD helper for native and paravirt platform Message-ID: <20120328142928.GE18161@phenom.dumpdata.com> References: <20120324003111.GA11777@andromeda.dapyr.net> <20120326163558.GC10236@phenom.dumpdata.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Source-IP: acsinet21.oracle.com [141.146.126.237] X-Auth-Type: Internal IP X-CT-RefId: str=0001.0A090204.4F732158.0088,ss=1,re=0.000,fgs=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 28, 2012 at 10:48:53AM +0000, Liu, Jinsong wrote: > >>> > >>> Liu, > >>> > >>> With this patch: " xen/enlighten: Expose MWAIT and MWAIT_LEAF if > >>> hypervisor OKs it." which is now in 3.4-rc0: > >>> (http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=blobdiff;f=arch/x86/xen/enlighten.c;h=b132ade26f778f2cfec7c2d5c7b6db48afe424d5;hp=4172af8ceeb363d06912af15bf89e8508752b794;hb=d4c6fa73fe984e504d52f3d6bba291fd76fe49f7;hpb=aab008db8063364dc3c8ccf4981c21124866b395) > >>> it means that now that the drivers/acpi/acpi_pad.c can run > >>> as is under Xen (as the MWAIT_LEAF is exposed) What is the impact > >>> of that? Is the monitor call causing a trap to the hypervisor which > >>> will ignore the call? Or will it have some more worrysome > >>> consequences? > >>> > >> > >> IMO this patch doesn't affect acpi_pad logic (both native and xen > >> acpi_pad). > > > > You are sure? The acpi_pad logic will now be activated so the native > > driver > > will run under Xen. My question is - what is the impact of that? > > I know what you mean now. What I mean is, w/ xen_acpi_pad patches, native acpi_pad only work under baremetal and xen_acpi_pad work under Xen (so no problem exposing mwait). What you mean is, w/o xen_acpi_pad patches, native acpi_pad will be actived under Xen and then risk occur ... I agree. Can you test that? And see what happens please? I don't have the hardware with _PUD. > > But just curious, what's the purpose and benefit of exposing mwait to dom0? I remember xen against doing so before. To expose deeper C-states to cstate.c so that xen-acpi-processor can then upload said states to the hypervisor. > > > > > My assumption is that the __monitor call will trap and we end up in > > the hypervisor - so that is not so bad, but not sure. > > Have you added code to hypervisor side (do_invalid_op)? if not, I think it would be problem (break dom0). Dom0 __monitor would trigger UD, then not handled by hypervisor, and bounce back to dom0 kernel, and kill itself. No, that is why I am asking you. > > But the point is, if exposing mwait, it would be risk for all logic which executed __monitor. So need add native_monitor/ xen_monitor. Argh. > > > > > But what I wonder is if what is the impact of the _OST call by the > > native driver? > > > > Say the firmware tells us - please offline 4 CPUS (we have eight). We > > enter 'acpi_pad_handle_notify' - create four threads, and each > > thread calls __monitor (which ends up in the hypervisor - and the > > hypervisor might not persue the __monitor call). > > > > During this time, the Linux kernel calls the _OST with 4 CPUs and .. > > > > what then? What happens if the _OST values are actually ignored (as > > it seems > > it would be in this case?) Is that OK? Or is that going to lead to the > > firmware turning off some of the cores anyhow? > > Hmm, if __monitor was tolerated silently as you assume, it would bring problem for _OST. What kind of problems? > > Thanks, > Jinsong > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xen.org > http://lists.xen.org/xen-devel