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 3CA08C02198 for ; Wed, 12 Feb 2025 18:32:03 +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=uy7nNmG2QRu1VTT14GwdMWSLsoZv24r+YKj1EbV0UcE=; b=IdBo6T7TODL10jaIZJovqpmDQk kMLoTaTaSm9LDH4jEljHMKqnNkRbUkshuH3cYhmzk9dn0Kkjc6eo3oSw4LKL8yGmDmAqrQFZxLqgC MppPHGyVP4hhoXSXsvrpmQRbtIq7VJpuDdXDAPV7IcDBErZs7ObZV40JRwVS7KfEPXXcNEL3aH/W7 2VmFb/ItBOGqqLcOjAI/zuerjilyTmRHz6VbehBNIL0mA2JX3zJkLLpETpIT8Q7Eya1wEHXb2oMyy 7mMoKbz6sI0GUlCdrenBZQr4QguDTi2uyvwvy9W+NvXjKEhvUeYprHrqRMm1mMTjOgPyg3SQAXJiJ K97HyDqw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tiHWb-00000008UKb-0Hoe; Wed, 12 Feb 2025 18:31:53 +0000 Received: from dfw.source.kernel.org ([139.178.84.217]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1tiHTa-00000008TYL-2Sr2 for linux-arm-kernel@lists.infradead.org; Wed, 12 Feb 2025 18:28:47 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id 833105C4B58; Wed, 12 Feb 2025 18:28:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1CD73C4CEDF; Wed, 12 Feb 2025 18:28:42 +0000 (UTC) Date: Wed, 12 Feb 2025 18:28:40 +0000 From: Catalin Marinas To: Zhenhua Huang Cc: anshuman.khandual@arm.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 v5] arm64: mm: Populate vmemmap/linear at the page level for hotplugged sections Message-ID: References: <20250109093824.452925-1-quic_zhenhuah@quicinc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250109093824.452925-1-quic_zhenhuah@quicinc.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250212_102846_714629_70BAD404 X-CRM114-Status: GOOD ( 23.73 ) 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 Thu, Jan 09, 2025 at 05:38:24PM +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. > > Considering the vmemmap_free -> unmap_hotplug_pmd_range path, when > pmd_sect() is true, the entire PMD section is cleared, even if there is > other effective subsection. For example page_struct_map1 and > page_strcut_map2 are part of a single PMD entry and they are hot-added > sequentially. Then page_struct_map1 is removed, vmemmap_free() will clear > the entire PMD entry freeing the struct page map for the whole section, > even though page_struct_map2 is still active. Similar problem exists > with linear mapping as well, for 16K base page(PMD size = 32M) or 64K > base page(PMD = 512M), their block mappings exceed SUBSECTION_SIZE. > Tearing down the entire PMD mapping too will leave other subsections > unmapped in the linear mapping. > > To address the issue, we need to prevent PMD/PUD/CONT mappings for both > linear and vmemmap for non-boot sections if corresponding size on the > given base page exceeds SUBSECTION_SIZE(2MB now). > > Cc: stable@vger.kernel.org # v5.4+ > Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug") > Signed-off-by: Zhenhua Huang > --- > Hi Catalin and Anshuman, > I have addressed comments so far, please help review. > One outstanding point which not finalized is in vmemmap_populate(): how to judge hotplug > section. Currently I am using system_state, discussion: > https://lore.kernel.org/linux-mm/1515dae4-cb53-4645-8c72-d33b27ede7eb@quicinc.com/ The patch looks fine to me, apart from one nit and a question below: > @@ -1339,9 +1349,27 @@ int arch_add_memory(int nid, u64 start, u64 size, > struct mhp_params *params) > { > int ret, flags = NO_EXEC_MAPPINGS; > + unsigned long start_pfn = PFN_DOWN(start); > + struct mem_section *ms = __pfn_to_section(start_pfn); > > VM_BUG_ON(!mhp_range_allowed(start, size, true)); > > + /* should not be invoked by early section */ > + WARN_ON(early_section(ms)); I don't remember the discussion, do we still need this warning here if the sections are not marked as early? I guess we can keep it if one does an arch_add_memory() on an early section. I think I suggested to use a WARN_ON_ONCE(!present_section()) but I completely forgot the memory hotplug code paths. > + > + /* > + * Disallow BlOCK/CONT mappings if the corresponding size exceeds Nit: capital L in BlOCK. Either way, Reviewed-by: Catalin Marinas