From 6710c287aebeb9837879e0108942f433e4f1ea46 Mon Sep 17 00:00:00 2001 From: Zhenhua Huang Date: Tue, 4 Mar 2025 15:27:00 +0800 Subject: [PATCH] UPSTREAM: arm64: mm: Populate vmemmap at the page level if not section aligned 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 Reviewed-by: Catalin Marinas Reviewed-by: Oscar Salvador Bug: 395030770 (cherry picked from commit d4234d131b0a3f9e65973f1cdc71bb3560f5d14b) Change-Id: I74d27f756c9941c4ea364759cb4b6bf3cda0c4e5 Signed-off-by: Zhenhua Huang