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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4F96FC53210 for ; Tue, 3 Jan 2023 17:46:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238159AbjACRpy (ORCPT ); Tue, 3 Jan 2023 12:45:54 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44534 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231270AbjACRps (ORCPT ); Tue, 3 Jan 2023 12:45:48 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 263E58E for ; Tue, 3 Jan 2023 09:45:47 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id B731A614A9 for ; Tue, 3 Jan 2023 17:45:46 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 27AA7C433EF; Tue, 3 Jan 2023 17:45:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1672767946; bh=3H6ZMjrHwXOXpPIiCTPQRckd0GNsBoWDroI24tfL8jo=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=g+4JQKE3Y98/Rjt49s2XeO4S875QW9jEuAJdtduU5js9tpaFrXSyM1xuyXsPrTDz3 /dGj5CevpXiFC93nlr9aqQPRt8yTjd9+A0KFq7vGTuLmWxbE9oYzOI/qwwEZaIKa3p kW5CbCTrSMyRXtKlv+bNxtipTmuwpSm1CprXAJCkCss1aSZr9oHHioZrXNnAHFhMI6 zje1bK9xc/38TQtYYLqkXT/BZ2WULexizhgxJlZ4joVAdlbZP5hYd8wpR9cQIEsGgH jW2XFtFk63cJ0bZac6UN2EJzCWS145CRZhaqSyQa1M81f5ItQ3qiFRu6nYg703uuia 9ji6DOo1hv0eQ== Received: from sofa.misterjones.org ([185.219.108.64] helo=goblin-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1pClM7-00GZvp-SC; Tue, 03 Jan 2023 17:45:44 +0000 Date: Tue, 03 Jan 2023 17:45:43 +0000 Message-ID: <86v8ln7bqw.wl-maz@kernel.org> From: Marc Zyngier To: Mukesh Ojha Cc: lkml Subject: Re: Query about IPI as NMI (pseudo-NMI) support patches In-Reply-To: References: <5bed08c5-8663-4e68-27b4-8b6d3957a880@quicinc.com> <86zgb07tfs.wl-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/28.2 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: quic_mojha@quicinc.com, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 03 Jan 2023 16:45:04 +0000, Mukesh Ojha wrote: > > Hi, > > Thanks for your reply. > > On 1/2/2023 10:41 PM, Marc Zyngier wrote: > > Hi Mukesh, > > > > On Mon, 02 Jan 2023 16:44:59 +0000, > > Mukesh Ojha wrote: > >> > >> Hi Marc, > >> > >> I was looking similar support mentioned in below patch series. > >> > >> https://lore.kernel.org/lkml/CAFA6WYO0+LQ=mB1spCstt0cNZ0G+sZu_+Wrv6BKSeXqF5SRq4A@mail.gmail.com/#t > >> > >> Wanted to check if there is chance of these patches to land in > >> mainline ? > > > > I certainly have no intention to merge it as is, specially as there is > > no good usage model for it other than "but think of debug!". > > > > We have exactly *one* SGI left. If we are going to lose it over such a > > feature, I'd want a description of how we are going to share it > > between potential users, and how we claw some currently used SGIs > > back. > > > But, looks like patch will fail if SGI is not available. > > https://lore.kernel.org/lkml/1604317487-14543-4-git-send-email-sumit.garg@linaro.org/ > > > > set_smp_ipi_range(base_sgi, 8); > > + if (n > nr_ipi) > + set_smp_dynamic_ipi(ipi_base + nr_ipi); > + > > So, static SGI allocation still has higher priority than dynamic > one. Would you be accepting if we keep it under some > CONFIG_ARM64_IPI_NMI_DEBUG ? But why should this thing have priority over other potential features? As I said above, there are two requirements: - being able to share a single NMI SGI amongst multiple users - being able to free existing SGIs in case we absolutely need an SGI for some other purposes In both cases, this is about making the SGI space scale *beyond* the 8 possible interrupts that we have. This needs to be solved to get something like this in. And I don't think hiding this behind an obscure "debug" configuration option that will get abused with out of tree stuff is a good move. Quite the opposite. Thanks, M. -- Without deviation from the norm, progress is not possible.