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=-10.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 136F6C433E3 for ; Fri, 21 Aug 2020 14:59:29 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A8815207BB for ; Fri, 21 Aug 2020 14:59:28 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="jJeL0ZxI" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A8815207BB Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 16BAE6B000E; Fri, 21 Aug 2020 10:59:28 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 11C8F6B0010; Fri, 21 Aug 2020 10:59:28 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 032A76B0022; Fri, 21 Aug 2020 10:59:27 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0206.hostedemail.com [216.40.44.206]) by kanga.kvack.org (Postfix) with ESMTP id E150E6B000E for ; Fri, 21 Aug 2020 10:59:27 -0400 (EDT) Received: from smtpin18.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 765AC801B26E for ; Fri, 21 Aug 2020 14:59:27 +0000 (UTC) X-FDA: 77174884374.18.clock44_2a153a22703a Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin18.hostedemail.com (Postfix) with ESMTP id 37CDA100ED0F8 for ; Fri, 21 Aug 2020 14:59:27 +0000 (UTC) X-HE-Tag: clock44_2a153a22703a X-Filterd-Recvd-Size: 8477 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf17.hostedemail.com (Postfix) with ESMTP for ; Fri, 21 Aug 2020 14:59:26 +0000 (UTC) Received: from localhost (104.sub-72-107-126.myvzw.com [72.107.126.104]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 028392078B; Fri, 21 Aug 2020 14:59:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598021965; bh=8SvRGeHN8PjzAryxcSzCn1l5HDCU4NdZCwvWwqwc/TQ=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=jJeL0ZxI40ABQG1jAcEoeCqJLVZEKr7JjT3mzYBSe1PXfwc2hMPToKPC+x1IXZpE0 /0Wq9hScOhWHwgEX8nX2N63lGlsmcSqwE58SsFRTuI8PdpDXmX/KwtCi29XSXy3bQb /VDM1rZFrz07C5BCGCqq3gH0endiZMgsFs/vReF8= Date: Fri, 21 Aug 2020 09:59:23 -0500 From: Bjorn Helgaas To: Jonathan Cameron Cc: linux-mm@kvack.org, linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, x86@kernel.org, Lorenzo Pieralisi , Bjorn Helgaas , rafael@kernel.org, linux-kernel@vger.kernel.org, Ingo Molnar , Thomas Gleixner , linuxarm@huawei.com, Dan Williams , Brice Goglin , Sean V Kelley , linux-api@vger.kernel.org, Keith Busch Subject: Re: [PATCH v9 4/6] ACPI: HMAT: Fix handling of changes from ACPI 6.2 to ACPI 6.3 Message-ID: <20200821145923.GA1625248@bjorn-Precision-5520> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200821134622.GA1620197@bjorn-Precision-5520> X-Rspamd-Queue-Id: 37CDA100ED0F8 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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); Bjorn