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=-11.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 autolearn=unavailable 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 67882C433E1 for ; Fri, 21 Aug 2020 16:33:56 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 34F7820724 for ; Fri, 21 Aug 2020 16:33:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="jd9QmwbL" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 34F7820724 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=Huawei.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=4F6LxSCvWA/FVHgw+4TqSbUrBFs9zwWrjgbofUoiypo=; b=jd9QmwbLE/EiPpw07gHbvShUz 2uf/RdGwQecMWZglxMZUrJ2uNA4VLPz3q4DCUBKblVshGcCldWhDZMwRxhjl26zrKoLYIM9j+HFob UEBRqOW6TKnyMEDrhP9HWRVQmrBjePga5nCg/kSVVpeIEZR6dfX4GZndwlZi/GimzX7QsSF7zQV2r QKUseiP1btsiTvilbwfhCbuDVAW5UOD4h52iiKKh4cRYolikIBkxjgu8rbKt/yylMNtydTyoU1CfM LMpPw4A1xvEk+Glie3S5sNAMxt9M2DpOJWU6bi3ecTYWdqil7J9IG9+ixeZjHs2EH64yym+USyyt3 eTYLKPQlg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1k99xh-0008KD-37; Fri, 21 Aug 2020 16:32:17 +0000 Received: from lhrrgout.huawei.com ([185.176.76.210] helo=huawei.com) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1k99xd-0008IQ-IR for linux-arm-kernel@lists.infradead.org; Fri, 21 Aug 2020 16:32:15 +0000 Received: from lhreml710-chm.china.huawei.com (unknown [172.18.7.107]) by Forcepoint Email with ESMTP id 03F623E9FE6DCAEF1E1E; Fri, 21 Aug 2020 17:32:10 +0100 (IST) Received: from localhost (10.52.123.86) by lhreml710-chm.china.huawei.com (10.201.108.61) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.1913.5; Fri, 21 Aug 2020 17:32:09 +0100 Date: Fri, 21 Aug 2020 17:30:37 +0100 From: Jonathan Cameron To: Bjorn Helgaas Subject: Re: [PATCH v9 4/6] ACPI: HMAT: Fix handling of changes from ACPI 6.2 to ACPI 6.3 Message-ID: <20200821173037.00007665@Huawei.com> In-Reply-To: <20200821145923.GA1625248@bjorn-Precision-5520> References: <20200821134622.GA1620197@bjorn-Precision-5520> <20200821145923.GA1625248@bjorn-Precision-5520> Organization: Huawei Technologies Research and Development (UK) Ltd. X-Mailer: Claws Mail 3.17.4 (GTK+ 2.24.32; i686-w64-mingw32) MIME-Version: 1.0 X-Originating-IP: [10.52.123.86] X-ClientProxiedBy: lhreml701-chm.china.huawei.com (10.201.108.50) To lhreml710-chm.china.huawei.com (10.201.108.61) X-CFilter-Loop: Reflected X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200821_123213_847625_8796C65A X-CRM114-Status: GOOD ( 50.10 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: rafael@kernel.org, Lorenzo Pieralisi , linux-acpi@vger.kernel.org, linux-api@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, linuxarm@huawei.com, Keith Busch , linux-mm@kvack.org, Ingo Molnar , Brice Goglin , Bjorn Helgaas , Thomas Gleixner , Dan Williams , linux-arm-kernel@lists.infradead.org, Sean V Kelley Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, 21 Aug 2020 09:59:23 -0500 Bjorn Helgaas wrote: > On Fri, Aug 21, 2020 at 08:46:22AM -0500, Bjorn Helgaas wrote: > > On Fri, Aug 21, 2020 at 01:59:01PM +0100, Jonathan Cameron wrote: > > > On Fri, 21 Aug 2020 07:13:56 -0500 > > > Bjorn Helgaas wrote: > > > > > > > [+cc Keith, author of 3accf7ae37a9 ("acpi/hmat: Parse and report > > > > heterogeneous memory")] > > > > > > > > On Fri, Aug 21, 2020 at 09:42:58AM +0100, Jonathan Cameron wrote: > > > > > On Thu, 20 Aug 2020 17:21:29 -0500 > > > > > Bjorn Helgaas wrote: > > > > > > > > > > > On Wed, Aug 19, 2020 at 10:51:09PM +0800, Jonathan Cameron wrote: > > > > > > > In ACPI 6.3, the Memory Proximity Domain Attributes Structure > > > > > > > changed substantially. One of those changes was that the flag > > > > > > > for "Memory Proximity Domain field is valid" was deprecated. > > > > > > > > > > > > > > This was because the field "Proximity Domain for the Memory" > > > > > > > became a required field and hence having a validity flag makes > > > > > > > no sense. > > > > > > > > > > > > > > So the correct logic is to always assume the field is there. > > > > > > > Current code assumes it never is. > > > > > > > > > > > > > > Signed-off-by: Jonathan Cameron > > > > > > > --- > > > > > > > drivers/acpi/numa/hmat.c | 2 +- > > > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > > > > > diff --git a/drivers/acpi/numa/hmat.c b/drivers/acpi/numa/hmat.c > > > > > > > index 2c32cfb72370..07cfe50136e0 100644 > > > > > > > --- a/drivers/acpi/numa/hmat.c > > > > > > > +++ b/drivers/acpi/numa/hmat.c > > > > > > > @@ -424,7 +424,7 @@ static int __init hmat_parse_proximity_domain(union acpi_subtable_headers *heade > > > > > > > pr_info("HMAT: Memory Flags:%04x Processor Domain:%u Memory Domain:%u\n", > > > > > > > p->flags, p->processor_PD, p->memory_PD); > > > > > > > > > > > > > > - if (p->flags & ACPI_HMAT_MEMORY_PD_VALID && hmat_revision == 1) { > > > > > > > + if ((p->flags & ACPI_HMAT_MEMORY_PD_VALID && hmat_revision == 1) || hmat_revision == 2) { > > > > > > > > > > > > I hope/assume the spec is written in such a way that p->memory_PD is > > > > > > required for any revision > 1? So maybe this should be: > > > > > > > > > > > > if ((p->flags & ACPI_HMAT_MEMORY_PD_VALID && hmat_revision == 1) || > > > > > > hmat_revision > 1) { > > > > > > > > I should have said simply: > > > > > > > > if (hmat_revision == 1 && p->flags & ACPI_HMAT_MEMORY_PD_VALID) > > > > > > > > We shouldn't even test p->flags for ACPI_HMAT_MEMORY_PD_VALID unless > > > > we already know it's revision 1. > > > > > > > > And unless there was a revision 0 of HMAT, there's no need to look for > > > > hmat_revison > 1. > > > > > > It needs to stay as an or statement as you had the first time. > > > The field is always valid for hmat_revision > 1, and valid for > > > hmat_revision == 1 with the flag set. You could express it as > > > > > > if ((p->flags & ACPI_HMAT_MEMORY_PD_VALID) || (hmat_revision != 1)) > > > > > > but that seems more confusing to me. > > > > Oh, you're right, sorry! There are two questions here: > > > > 1) In what order should we test "p->flags & ACPI_HMAT_MEMORY_PD_VALID" > > and "hmat_revision == 1"? ACPI_HMAT_MEMORY_PD_VALID is defined > > only when "hmat_revision == 1", so I think we should test the > > revision first. > > > > When "hmat_revision == 2", ACPI_HMAT_MEMORY_PD_VALID is reserved, > > so we shouldn't test it, even if we later check the revision and > > discard the result of the flag test. This is a tiny thing, > > admittedly, but I think it follows the spec more clearly. > > > > 2) Do we need to test hmat_revision for anything other than 1? Yes, > > you're right, see below. > > > > > > > Good point. We have existing protections elsewhere against > > > > > hmat_revision being anything other than 1 or 2, so we should aim to > > > > > keep that in only one place. > > > > > > > > I think the "Ignoring HMAT: Unknown revision" test in hmat_init(), > > > > added by 3accf7ae37a9 ("acpi/hmat: Parse and report heterogeneous > > > > memory"), is a mistake. > > > > > > > > And I think hmat_normalize() has a similar mistake in that it tests > > > > explicitly for hmat_revision == 2 when it should accept 2 AND anything > > > > later. > > > > > > > > We should assume that future spec revisions will be backwards > > > > compatible. Otherwise we're forced to make kernel changes when we > > > > otherwise would not have to. > > > > > > I disagree with this. There is no rule in ACPI about maintaining > > > backwards compatibility. The assumption is that the version number > > > will always be checked. The meaning of fields changed between > > > version 1 and version 2 so it would be bold to assume that won't > > > happen in the future! > > > > There *is* a rule about maintaining backwards compatibility. ACPI > > v6.3, sec 5.2.2, says: > > > > All versions of the ACPI tables must maintain backward > > compatibility. To accomplish this, modifications of the tables > > consist of redefinition of previously reserved fields and values > > plus appending data to the 1.0 tables. Modifications of the ACPI > > tables require that the version numbers of the modified tables be > > incremented. > > > > > HMAT is an optional table, so if someone boots up an old kernel > > > they are probably better off failing to use it at all than > > > misinterpreting it. > > > > An old kernel tests: > > > > if (p->flags & ACPI_HMAT_MEMORY_PD_VALID && hmat_revision == 1) > > target = find_mem_target(p->memory_PD); > > > > which is fine on old firmware. On new firmware (hmat_revision == 2), > > it will ignore p->memory_PD. That is probably a problem, but I think > > we should check for that at the place where we need a memory_PD and > > don't find one. That's more general than sanity checking a revision. > > > > A new kernel that tests: > > > > if ((hmat_revision == 1 && p->flags & ACPI_HMAT_MEMORY_PD_VALID) || > > hmat_revision > 1) > > target = find_mem_target(p->memory_PD); > > > > will do the right thing on both old and new firmware. > > Actually, I think this part of the spec was done incorrectly. > > ACPI v6.3 could have made the p->memory_PD field required without > changing the definition of ACPI_HMAT_MEMORY_PD_VALID. What value was > gained by making ACPI_HMAT_MEMORY_PD_VALID a reserved bit in v6.3? > > If they had left ACPI_HMAT_MEMORY_PD_VALID alone, the Linux code could > have been simply this, which would work with old firmware and new > firmware, and we wouldn't have to touch this at all: > > if (p->flags & ACPI_HMAT_MEMORY_PD_VALID) > target = find_mem_target(p->memory_PD); I have a slight recollection that might have been my fault :) Oops. Jonathan > > Bjorn _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel