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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5F684C28B24 for ; Wed, 5 Mar 2025 20:18:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=CTT4VlJeLCC6/l/jodN5fkT+Y2Y1zsiD3qYQ2wYCV1c=; b=UHQJTzqTDq8NkkAF9+Fgd8gzGu Y+Ft/NAD5L1MA36RgNmq4o8Lyk/L2AlztNqPs1R9/OtekA4TmIZwBI7ENDozHSD/gUFFalG/obAP7 +yrZi8+1tfgHf5vGlMJn6fOAa32KBC2Vl9s2PAY/Rx3p8VZ/tkYnKKXa9h0TTD+ccPzcGBG5ZNaea xuRmCisIiAa2PybSA9WC50x04zkci0mVGjc8whP6HdvEEMlMfUSpXbAo0sY8fMQW90jC2ayBza+Us yDUJ3maKV6s1cTtQ4ksgc4wMWv/fybVG59m6yIqrQiBiJpy4ge6Jgt60IYhQVAshAZVvAADjTUSbn 2Fj2K77g==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tpvCZ-00000009C1i-0oed; Wed, 05 Mar 2025 20:18:47 +0000 Received: from nyc.source.kernel.org ([2604:1380:45d1:ec00::3]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1tpty9-000000090D4-33Wl for linux-arm-kernel@lists.infradead.org; Wed, 05 Mar 2025 18:59:50 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by nyc.source.kernel.org (Postfix) with ESMTP id BA10DA45F6E; Wed, 5 Mar 2025 18:54:17 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5ADD8C4CED1; Wed, 5 Mar 2025 18:59:45 +0000 (UTC) Date: Wed, 5 Mar 2025 18:59:43 +0000 From: Catalin Marinas To: Zhenhua Huang Cc: anshuman.khandual@arm.com, david@redhat.com, will@kernel.org, ardb@kernel.org, ryan.roberts@arm.com, mark.rutland@arm.com, joey.gouly@arm.com, dave.hansen@linux.intel.com, akpm@linux-foundation.org, chenfeiyang@loongson.cn, chenhuacai@kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, quic_tingweiz@quicinc.com, stable@vger.kernel.org Subject: Re: [PATCH v9] arm64: mm: Populate vmemmap at the page level if not section aligned Message-ID: References: <20250304072700.3405036-1-quic_zhenhuah@quicinc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250304072700.3405036-1-quic_zhenhuah@quicinc.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250305_105949_834635_C4C9258F X-CRM114-Status: GOOD ( 23.17 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Mar 04, 2025 at 03:27:00PM +0800, Zhenhua Huang wrote: > On the arm64 platform with 4K base page config, SECTION_SIZE_BITS is set > to 27, making one section 128M. The related page struct which vmemmap > points to is 2M then. > Commit c1cc1552616d ("arm64: MMU initialisation") optimizes the > vmemmap to populate at the PMD section level which was suitable > initially since hot plug granule is always one section(128M). However, > commit ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug") > introduced a 2M(SUBSECTION_SIZE) hot plug granule, which disrupted the > existing arm64 assumptions. > > The first problem is that if start or end is not aligned to a section > boundary, such as when a subsection is hot added, populating the entire > section is wasteful. > > The next problem is if we hotplug something that spans part of 128 MiB > section (subsections, let's call it memblock1), and then hotplug something > that spans another part of a 128 MiB section(subsections, let's call it > memblock2), and subsequently unplug memblock1, vmemmap_free() will clear > the entire PMD entry which also supports memblock2 even though memblock2 > is still active. > > Assuming hotplug/unplug sizes are guaranteed to be symmetric. Do the > fix similar to x86-64: populate to pages levels if start/end is not aligned > with section boundary. > > Cc: # v5.4+ > Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug") > Acked-by: David Hildenbrand > Signed-off-by: Zhenhua Huang > --- > arch/arm64/mm/mmu.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) Reviewed-by: Catalin Marinas Will, another bug that has been around for ages. Do you want to take it as a fix? > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index b4df5bc5b1b8..1dfe1a8efdbe 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -1177,8 +1177,11 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node, > struct vmem_altmap *altmap) > { > WARN_ON((start < VMEMMAP_START) || (end > VMEMMAP_END)); > + /* [start, end] should be within one section */ > + WARN_ON_ONCE(end - start > PAGES_PER_SECTION * sizeof(struct page)); > > - if (!IS_ENABLED(CONFIG_ARM64_4K_PAGES)) > + if (!IS_ENABLED(CONFIG_ARM64_4K_PAGES) || > + (end - start < PAGES_PER_SECTION * sizeof(struct page))) > return vmemmap_populate_basepages(start, end, node, altmap); > else > return vmemmap_populate_hugepages(start, end, node, altmap); > -- > 2.25.1 > -- Catalin