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arm64: mm: Populate vmemmap at the page level if not section aligned

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commit d4234d131b0a3f9e65973f1cdc71bb3560f5d14b upstream.

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 c1cc155261 ("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 ba72b4c8cf ("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: stable@vger.kernel.org # v5.4+
Fixes: ba72b4c8cf ("mm/sparsemem: support sub-section hotplug")
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Zhenhua Huang <quic_zhenhuah@quicinc.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20250304072700.3405036-1-quic_zhenhuah@quicinc.com
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Zhenhua Huang
2025-03-04 15:27:00 +08:00
committed by Greg Kroah-Hartman
parent 5a87e46da2
commit f6bbea2ffe
1 changed files with 4 additions and 1 deletions
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5
arch/arm64/mm/mmu.c
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@@ -1176,8 +1176,11 @@ 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);