From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [IPv6:2401:3900:2:1::2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 751C31A1E05 for ; Wed, 2 Sep 2015 15:10:15 +1000 (AEST) Received: from e19.ny.us.ibm.com (e19.ny.us.ibm.com [129.33.205.209]) (using TLSv1 with cipher CAMELLIA256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id F2CB51401F0 for ; Wed, 2 Sep 2015 15:10:13 +1000 (AEST) Received: from /spool/local by e19.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 2 Sep 2015 01:10:11 -0400 Received: from b01cxnp23032.gho.pok.ibm.com (b01cxnp23032.gho.pok.ibm.com [9.57.198.27]) by d01dlp02.pok.ibm.com (Postfix) with ESMTP id 9962B6E804F for ; Wed, 2 Sep 2015 01:01:53 -0400 (EDT) Received: from d01av02.pok.ibm.com (d01av02.pok.ibm.com [9.56.224.216]) by b01cxnp23032.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id t825A9vp61472994 for ; Wed, 2 Sep 2015 05:10:09 GMT Received: from d01av02.pok.ibm.com (localhost [127.0.0.1]) by d01av02.pok.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id t825A6uf006374 for ; Wed, 2 Sep 2015 01:10:08 -0400 Date: Wed, 2 Sep 2015 10:39:58 +0530 From: Ananth N Mavinakayanahalli To: Scott Wood Cc: Michael Ellerman , , "Paul Mackerras" , Subject: Re: powerpc: Add user-return-notifier support Message-ID: <20150902050958.GC1196@in.ibm.com> Reply-To: ananth@in.ibm.com References: <20150825054110.GD3815@in.ibm.com> <20150831103517.96D1A1401E7@ozlabs.org> <20150901064113.GA1196@in.ibm.com> <1441152192.4966.103.camel@freescale.com> <20150902023713.GB1196@in.ibm.com> <1441164552.4966.153.camel@freescale.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1441164552.4966.153.camel@freescale.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, Sep 01, 2015 at 10:29:12PM -0500, Scott Wood wrote: > On Wed, 2015-09-02 at 08:07 +0530, Ananth N Mavinakayanahalli wrote: > > On Tue, Sep 01, 2015 at 07:03:12PM -0500, Scott Wood wrote: > > > On Tue, 2015-09-01 at 12:11 +0530, Ananth N Mavinakayanahalli wrote: > > > > On Mon, Aug 31, 2015 at 08:35:17PM +1000, Michael Ellerman wrote: > > > > > On Tue, 2015-25-08 at 05:41:10 UTC, Ananth N Mavinakayanahalli wrote: ... > > > > We could certainly make this a generic config option.. but I am yet to > > > > see a real usecase outside of the KVM thingy. We do use TIF_UPROBE for > > > > something very similar, though that needs to fire much before the > > > > outstanding signals get handled. The user-return notifier is the last > > > > thing executed before return to userspace -- the two cannot be merged. > > > > > > > > Ananth > > > > > > > > PS: I am not sure having an 'ok' against the Documentation/features/ for > > > > powerpc is a valid enough argument for this :-) > > > > > > So how did you test this? What platforms did you test it on? What > > > hardware > > > support does it need? > > > > Simple kernel module below... Its fairly evident from the patch that the > > feature is a software only construct and no specific hardware support is > > needed. > > It's evident now that I'm aware of what the purpose is... It wasn't 100% > > clear before, at least from a quick glance, given that the explanation was > > "look at this hardware-specific KVM patch", whether there was an assumption > of something else going on -- and even things that are implemented in > software often work differently on book3s versus book3e, ppc32 versus ppc64, > etc. I meant the infrastructure is agnostic of the underlying Power platform. Sorry if I wasn't clear. > Why is this selected by KVM on PPC if KVM on PPC doesn't use it? What is the > user you're trying to enable? I copied Paul and Gautham to get their thoughts on whether it is something they could use on Power. At this time, apart from enabling the feature, I do not have a specific usecase for it. We can park this patch pending a real user on powerpc. > Where is the "profiler" that Documentation/features/debug/user-ret- > profiler/arch-support.txt hints at? I guess profiler is a misnomer. Not sure why it was named that and not a notifier. Ananth