[PATCH 5.10 4/5] arm: extend pfn_valid to take into account freed memory map alignment

[Mark-PK Tsai <mark-pk.tsai@mediatek.com>]

From: Mike Rapoport <rppt@linux.ibm.com>

[ Upstream commit a4d5613c4dc6d413e0733e37db9d116a2a36b9f3 ]

When unused memory map is freed the preserved part of the memory map is
extended to match pageblock boundaries because lots of core mm
functionality relies on homogeneity of the memory map within pageblock
boundaries.

Since pfn_valid() is used to check whether there is a valid memory map
entry for a PFN, make it return true also for PFNs that have memory map
entries even if there is no actual memory populated there.

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Tested-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/lkml/20210630071211.21011-1-rppt@kernel.org/
Signed-off-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com>
---
 arch/arm/mm/init.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 7fd049cbc5b0..15af4dd52426 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -125,11 +125,22 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max_low,
 int pfn_valid(unsigned long pfn)
 {
 	phys_addr_t addr = __pfn_to_phys(pfn);
+	unsigned long pageblock_size = PAGE_SIZE * pageblock_nr_pages;
 
 	if (__phys_to_pfn(addr) != pfn)
 		return 0;
 
-	return memblock_is_map_memory(addr);
+	/*
+	 * If address less than pageblock_size bytes away from a present
+	 * memory chunk there still will be a memory map entry for it
+	 * because we round freed memory map to the pageblock boundaries.
+	 */
+	if (memblock_overlaps_region(&memblock.memory,
+				     ALIGN_DOWN(addr, pageblock_size),
+				     pageblock_size))
+		return 1;
+
+	return 0;
 }
 EXPORT_SYMBOL(pfn_valid);
 #endif
-- 
2.18.0