arm64: mm: Fix initialisation of DMA zones on non-NUMA systems

John reports that the recently merged commit 1a8e1cef ("arm64: use
both ZONE_DMA and ZONE_DMA32") breaks the boot on his DB845C board:

  | Booting Linux on physical CPU 0x0000000000 [0x517f803c]
  | Linux version 5.4.0-mainline-10675-g957a03b9e38f
  | Machine model: Thundercomm Dragonboard 845c
  | [...]
  | Built 1 zonelists, mobility grouping on.  Total pages: -188245
  | Kernel command line: earlycon
  | firmware_class.path=/vendor/firmware/ androidboot.hardware=db845c
  | init=/init androidboot.boot_devices=soc/1d84000.ufshc
  | printk.devkmsg=on buildvariant=userdebug root=/dev/sda2
  | androidboot.bootdevice=1d84000.ufshc androidboot.serialno=c4e1189c
  | androidboot.baseband=sda
  | msm_drm.dsi_display0=dsi_lt9611_1080_video_display:
  | androidboot.slot_suffix=_a skip_initramfs rootwait ro init=/init
  |
  | <hangs indefinitely here>

This is because, when CONFIG_NUMA=n, zone_sizes_init() fails to handle
memblocks that fall entirely within the ZONE_DMA region and erroneously ends up
trying to add a negatively-sized region into the following ZONE_DMA32, which is
later interpreted as a large unsigned region by the core MM code.

Rework the non-NUMA implementation of zone_sizes_init() so that the start
address of the memblock being processed is adjusted according to the end of the
previous zone, which is then range-checked before updating the hole information
of subsequent zones.

Cc: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/lkml/CALAqxLVVcsmFrDKLRGRq7GewcW405yTOxG=KR3csVzQ6bXutkA@mail.gmail.com
Fixes: 1a8e1cef ("arm64: use both ZONE_DMA and ZONE_DMA32")
Reported-by: John Stultz <john.stultz@linaro.org>
Tested-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/mm/init.c

@@ -214,15 +214,14 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
 {
 	struct memblock_region *reg;
 	unsigned long zone_size[MAX_NR_ZONES], zhole_size[MAX_NR_ZONES];
-	unsigned long max_dma32 = min;
-	unsigned long __maybe_unused max_dma = min;
+	unsigned long __maybe_unused max_dma, max_dma32;
 
 	memset(zone_size, 0, sizeof(zone_size));
 
+	max_dma = max_dma32 = min;
 #ifdef CONFIG_ZONE_DMA
-	max_dma = PFN_DOWN(arm64_dma_phys_limit);
+	max_dma = max_dma32 = PFN_DOWN(arm64_dma_phys_limit);
 	zone_size[ZONE_DMA] = max_dma - min;
-	max_dma32 = max_dma;
 #endif
 #ifdef CONFIG_ZONE_DMA32
 	max_dma32 = PFN_DOWN(arm64_dma32_phys_limit);
@@ -236,25 +235,23 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max)
 		unsigned long start = memblock_region_memory_base_pfn(reg);
 		unsigned long end = memblock_region_memory_end_pfn(reg);
 
-		if (start >= max)
-			continue;
 #ifdef CONFIG_ZONE_DMA
-		if (start < max_dma) {
-			unsigned long dma_end = min_not_zero(end, max_dma);
+		if (start >= min && start < max_dma) {
+			unsigned long dma_end = min(end, max_dma);
 			zhole_size[ZONE_DMA] -= dma_end - start;
+			start = dma_end;
 		}
 #endif
 #ifdef CONFIG_ZONE_DMA32
-		if (start < max_dma32) {
+		if (start >= max_dma && start < max_dma32) {
 			unsigned long dma32_end = min(end, max_dma32);
-			unsigned long dma32_start = max(start, max_dma);
-			zhole_size[ZONE_DMA32] -= dma32_end - dma32_start;
+			zhole_size[ZONE_DMA32] -= dma32_end - start;
+			start = dma32_end;
 		}
 #endif
-		if (end > max_dma32) {
+		if (start >= max_dma32 && start < max) {
 			unsigned long normal_end = min(end, max);
-			unsigned long normal_start = max(start, max_dma32);
-			zhole_size[ZONE_NORMAL] -= normal_end - normal_start;
+			zhole_size[ZONE_NORMAL] -= normal_end - start;
 		}
 	}