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 3DCC525E446; Wed, 12 Feb 2025 18:28:45 +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=1739384926; cv=none; b=oETWMoq28JmpP5nDad7+5vY70HgQSNextQn7emqITd6CLFF6Ead3G9VVajY1y/qwXB4TQGG/PWK9sqTDzSF/DYZViDd90xf24As0F8R4n0rfDV8OiLFspKV+6iufs/L/JRaGs8ags6aOxXrAJRS5btIkE0+of6Pk6PmOPJaL08I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739384926; c=relaxed/simple; bh=MEkWB4ja2rW/5DxYBYUfS8Zpe+WMG31MnhY7TpmVYNw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=BAlUqLsRKv19v5rQEzWU0ebjTw471rd6s9+dYfeYTzzDuEtzocyuyWfsiPagsP0EdOheCTUkJzrWSaj0CIAdsCU9Rzyw5QHW7GeYHFyzTJS1fTixvfrhvBzcVFGaFjXRKVJdtn68WKUCPUmn9OlT57mxgTixTGkU+vaRRzQjAJ8= 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 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> 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: <20250109093824.452925-1-quic_zhenhuah@quicinc.com> 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