From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 01C19ECDE5F for ; Fri, 20 Jul 2018 00:27:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 87EC72084C for ; Fri, 20 Jul 2018 00:27:15 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 87EC72084C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=neuling.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731175AbeGTBMs convert rfc822-to-8bit (ORCPT ); Thu, 19 Jul 2018 21:12:48 -0400 Received: from ozlabs.org ([203.11.71.1]:33515 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730798AbeGTBMs (ORCPT ); Thu, 19 Jul 2018 21:12:48 -0400 Received: from localhost.localdomain (localhost [127.0.0.1]) by ozlabs.org (Postfix) with ESMTP id 41WsCM090qz9s4r; Fri, 20 Jul 2018 10:27:11 +1000 (AEST) Received: by localhost.localdomain (Postfix, from userid 1000) id B9F28EE78BF; Fri, 20 Jul 2018 10:27:10 +1000 (AEST) Message-ID: <1205bfc10c62986b4345fa258cf37e820c08226b.camel@neuling.org> Subject: Re: [RESEND][PATCH] powerpc/powernv : Save/Restore SPRG3 on entry/exit from stop. From: Michael Neuling To: ego@linux.vnet.ibm.com Cc: Michael Ellerman , Benjamin Herrenschmidt , Vaidyanathan Srinivasan , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, Florian Weimer , Oleg Nesterov Date: Fri, 20 Jul 2018 10:27:10 +1000 In-Reply-To: <20180718081249.GA17700@in.ibm.com> References: <1531826849-31838-1-git-send-email-ego@linux.vnet.ibm.com> <1531843216-22209-1-git-send-email-ego@linux.vnet.ibm.com> <80bbdf47081e3e302ab5f28b5ddc9e2faabba842.camel@neuling.org> <20180718081249.GA17700@in.ibm.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT X-Mailer: Evolution 3.28.1-2 Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2018-07-18 at 13:42 +0530, Gautham R Shenoy wrote: > Hello Mikey, > > On Wed, Jul 18, 2018 at 09:24:19AM +1000, Michael Neuling wrote: > > > > > DEFINE(PPC_DBELL_SERVER, PPC_DBELL_SERVER); > > > diff --git a/arch/powerpc/kernel/idle_book3s.S > > > b/arch/powerpc/kernel/idle_book3s.S > > > index d85d551..5069d42 100644 > > > --- a/arch/powerpc/kernel/idle_book3s.S > > > +++ b/arch/powerpc/kernel/idle_book3s.S > > > @@ -120,6 +120,9 @@ power9_save_additional_sprs: > > > mfspr r4, SPRN_MMCR2 > > > std r3, STOP_MMCR1(r13) > > > std r4, STOP_MMCR2(r13) > > > + > > > + mfspr r3, SPRN_SPRG3 > > > + std r3, STOP_SPRG3(r13) > > > > We don't need to save it. Just restore it from paca->sprg_vdso which should > > never change. > > Ok. I will respin a patch to restore SPRG3 from paca->sprg_vdso. > > > > > How can we do better at catching these missing SPRGs? > > We can go through the list of SPRs from the POWER9 User Manual and > document explicitly why we don't have to save/restore certain SPRs > during the execution of the stop instruction. Does this sound ok ? > > (Ref: Table 4-8, Section 4.7.3.4 from the POWER9 User Manual > accessible from > https://openpowerfoundation.org/?resource_lib=power9-processor-users-manual) I was thinking of a boot time test case built into linux. linux has some boot time test cases which you can enable via CONFIG options. Firstly you could see if an SPR exists using the same trick xmon does in dump_one_spr(). Then once you have a list of usable SPRs, you could write all the known ones (I assume you'd have to leave out some, like the PSSCR), then set the appropriate stop level, make sure you got into that stop level, and then see if that register was changed. Then you'd have an automated list of registers you need to make sure you save/restore at each stop level. Could something like that work? Mikey