[PATCH] arm64: Ignore any DMA offsets in the max_zone_phys() calculation

[Catalin Marinas]

Currently, the kernel assumes that if RAM starts above 32-bit (or
zone_bits), there is still a ZONE_DMA/DMA32 at the bottom of the RAM and
such constrained devices have a hardwired DMA offset. In practice, we
haven't noticed any such hardware so let's assume that we can expand
ZONE_DMA32 to the available memory if no RAM below 4GB. Similarly,
ZONE_DMA is expanded to the 4GB limit if no RAM addressable by
zone_bits.

Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
---
 arch/arm64/mm/init.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 095540667f0f..362160e16fb2 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -175,14 +175,21 @@ static void __init reserve_elfcorehdr(void)
 #endif /* CONFIG_CRASH_DUMP */
 
 /*
- * Return the maximum physical address for a zone with a given address size
- * limit. It currently assumes that for memory starting above 4G, 32-bit
- * devices will use a DMA offset.
+ * Return the maximum physical address for a zone accessible by the given bits
+ * limit. If the DRAM starts above 32-bit, expand the zone to the maximum
+ * available memory, otherwise cap it at 32-bit.
  */
 static phys_addr_t __init max_zone_phys(unsigned int zone_bits)
 {
-	phys_addr_t offset = memblock_start_of_DRAM() & GENMASK_ULL(63, zone_bits);
-	return min(offset + (1ULL << zone_bits), memblock_end_of_DRAM());
+	phys_addr_t zone_mask = (1ULL << zone_bits) - 1;
+	phys_addr_t phys_start = memblock_start_of_DRAM();
+
+	if (!(phys_start & U32_MAX))
+		zone_mask = PHYS_ADDR_MAX;
+	else if (!(phys_start & zone_mask))
+		zone_mask = U32_MAX;
+
+	return min(zone_mask + 1, memblock_end_of_DRAM());
 }
 
 static void __init zone_sizes_init(unsigned long min, unsigned long max)