arm64: Fix /proc/iomem for reserved but not memory regions

We describe ranges of 'reserved' memory to userspace via /proc/iomem.
Commit 50d7ba36b9 ("arm64: export memblock_reserve()d regions via
/proc/iomem") updated the logic to export regions that were reserved
because their contents should be preserved. This allowed kexec-tools
to tell the difference between 'reserved' memory that must be
preserved and not overwritten, (e.g. the ACPI tables), and 'nomap'
memory that must not be touched without knowing the memory-attributes
(e.g. RAS CPER regions).

The above commit wrongly assumed that memblock_reserve() would not
be used to reserve regions that aren't memory. It turns out this is
exactly what early_init_dt_reserve_memory_arch() will do if it finds
a DT reserved-memory that was also carved out of the memory node, which
results in a WARN_ON_ONCE() and the region being reserved instead of
ignored. The ramoops description on hikey and dragonboard-410c both do
this, so we can't simply write this configuration off as "buggy firmware".

Avoid this issue by rewriting reserve_memblock_reserved_regions() so
that only the portions of reserved regions which overlap with mapped
memory are actually reserved.

Fixes: 50d7ba36b9 ("arm64: export memblock_reserve()d regions via /proc/iomem")
Reported-by: John Stultz <john.stultz@linaro.org>
Reported-by: Paolo Pisati <p.pisati@gmail.com>
CC: Akashi Takahiro <takahiro.akashi@linaro.org>
CC: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: James Morse <james.morse@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/setup.c

@@ -64,6 +64,9 @@
 #include <asm/xen/hypervisor.h>
 #include <asm/mmu_context.h>
 
+static int num_standard_resources;
+static struct resource *standard_resources;
+
 phys_addr_t __fdt_pointer __initdata;
 
 /*
@@ -206,14 +209,19 @@ static void __init request_standard_resources(void)
 {
 	struct memblock_region *region;
 	struct resource *res;
+	unsigned long i = 0;
 
 	kernel_code.start   = __pa_symbol(_text);
 	kernel_code.end     = __pa_symbol(__init_begin - 1);
 	kernel_data.start   = __pa_symbol(_sdata);
 	kernel_data.end     = __pa_symbol(_end - 1);
 
+	num_standard_resources = memblock.memory.cnt;
+	standard_resources = alloc_bootmem_low(num_standard_resources *
+					       sizeof(*standard_resources));
+
 	for_each_memblock(memory, region) {
-		res = alloc_bootmem_low(sizeof(*res));
+		res = &standard_resources[i++];
 		if (memblock_is_nomap(region)) {
 			res->name  = "reserved";
 			res->flags = IORESOURCE_MEM;
@@ -243,36 +251,26 @@ static void __init request_standard_resources(void)
 
 static int __init reserve_memblock_reserved_regions(void)
 {
-	phys_addr_t start, end, roundup_end = 0;
-	struct resource *mem, *res;
-	u64 i;
+	u64 i, j;
 
-	for_each_reserved_mem_region(i, &start, &end) {
-		if (end <= roundup_end)
-			continue; /* done already */
+	for (i = 0; i < num_standard_resources; ++i) {
+		struct resource *mem = &standard_resources[i];
+		phys_addr_t r_start, r_end, mem_size = resource_size(mem);
 
-		start = __pfn_to_phys(PFN_DOWN(start));
-		end = __pfn_to_phys(PFN_UP(end)) - 1;
-		roundup_end = end;
-
-		res = kzalloc(sizeof(*res), GFP_ATOMIC);
-		if (WARN_ON(!res))
-			return -ENOMEM;
-		res->start = start;
-		res->end = end;
-		res->name  = "reserved";
-		res->flags = IORESOURCE_MEM;
-
-		mem = request_resource_conflict(&iomem_resource, res);
-		/*
-		 * We expected memblock_reserve() regions to conflict with
-		 * memory created by request_standard_resources().
-		 */
-		if (WARN_ON_ONCE(!mem))
+		if (!memblock_is_region_reserved(mem->start, mem_size))
 			continue;
-		kfree(res);
 
-		reserve_region_with_split(mem, start, end, "reserved");
+		for_each_reserved_mem_region(j, &r_start, &r_end) {
+			resource_size_t start, end;
+
+			start = max(PFN_PHYS(PFN_DOWN(r_start)), mem->start);
+			end = min(PFN_PHYS(PFN_UP(r_end)) - 1, mem->end);
+
+			if (start > mem->end || end < mem->start)
+				continue;
+
+			reserve_region_with_split(mem, start, end, "reserved");
+		}
 	}
 
 	return 0;