arm64: mm: update max_dma32 before calculating size of NORMAL zone

Commit f483a853 ("arm64: mm: fix booting on systems with no memory
below 4GB") sets max_dma32 to the minimum of the maximum pfn and
MAX_DMA32_PFN. This value is later used as the base of the NORMAL zone,
which is incorrect when MAX_DMA32_PFN is below the minimum pfn (i.e. all
memory is above 4GB).

This patch fixes the problem by ensuring that max_dma32 is always set to
the end of the DMA32 zone.
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/mm/init.c

@@ -79,8 +79,8 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
 
 #ifdef CONFIG_ZONE_DMA32
 	/* 4GB maximum for 32-bit only capable devices */
-	max_dma32 = min(max, MAX_DMA32_PFN);
-	zone_size[ZONE_DMA32] = max(min, max_dma32) - min;
+	max_dma32 = max(min, min(max, MAX_DMA32_PFN));
+	zone_size[ZONE_DMA32] = max_dma32 - min;
 #endif
 	zone_size[ZONE_NORMAL] = max - max_dma32;