arm64/mm: Check the requested PFN range during memory removal

prevent_memory_remove_notifier() advances pfn while scanning the requested
range for early memory. When the loop completes, pfn is at or beyond
end_pfn. Passing it to can_unmap_without_split() therefore checks a range
after the one being offlined.

Consequently, a valid request can be rejected based on the following
range, while a request that would split a leaf mapping can be accepted if
the shifted range can be unmapped without a split. This was observed with
CXL DAX memory, where the final memory block was incorrectly allowed to
be offlined.

Pass arg->start_pfn into can_unmap_without_split() so it checks the
requested range.

Fixes: 95a58852b0e5 ("arm64/mm: Reject memory removal that splits a kernel leaf mapping")
Signed-off-by: Richard Cheng <icheng@nvidia.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index a25d8beacc83..18a8b0d3714e 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -2194,7 +2194,7 @@ static int prevent_memory_remove_notifier(struct notifier_block *nb,
 		}
 	}
 
-	if (!can_unmap_without_split(pfn, arg->nr_pages))
+	if (!can_unmap_without_split(arg->start_pfn, arg->nr_pages))
 		return NOTIFY_BAD;
 
 	return NOTIFY_OK;