From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B4A02257424; Wed, 5 Mar 2025 18:59:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741201188; cv=none; b=bbrrL2gHcDeEedLXObzdg9phWIkOlEXdO1ouEegD8oMgl2Z3P54l7LkGtkJ+BucTPEIPWO0MT1ykR8tDH7j5/qHRpwSgcTc8sEDSEQ7J0rw0Zb2Xi10K6LXPhvSZVtYg8QkTg5eef6jzERChIyYzhuGZb92Vqv3/XXAToHOMD4Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741201188; c=relaxed/simple; bh=KOntfY2GF79iwDM2QQoQy22zDcX3Cb1Ne2iCHZjE6+w=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=jnUssadkE74NfTaj+dTB858lFyM45hCkVYpowxWmufb9bZ/z2uyp2iAxhCheQLvXNkbUzpCKu9Z+npOVisV4QeZYA8TUDBt7rZEVu/GsMo4HiijtVtcYaHjD9VuEdfN/eGUia7O4VBa/WTi6x3cFNIg2HKDi6CDsH2TGVEz0SO0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 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> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250304072700.3405036-1-quic_zhenhuah@quicinc.com> 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