[PATCH 5.10 011/101] arm64: Ignore any DMA offsets in the max_zone_phys() calculation

[Sasha Levin]

From: Catalin Marinas <catalin.marinas@xxxxxxx>

commit 791ab8b2e3db0c6e4295467d10398800ec29144c upstream.

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>
Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
Reviewed-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
Cc: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
Cc: Robin Murphy <robin.murphy@xxxxxxx>
Link: https://lore.kernel.org/r/20201118185809.1078362-1-catalin.marinas@xxxxxxx
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 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 a985d292e820..c0a7f0d90b39 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -174,14 +174,21 @@ 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 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 = DMA_BIT_MASK(zone_bits);
+	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, memblock_end_of_DRAM() - 1) + 1;
 }
 
 static void __init zone_sizes_init(unsigned long min, unsigned long max)
-- 
2.30.2