1 files changed, 34 insertions, 9 deletions

diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 57120f0749cc..c3acbd26408b 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -753,22 +753,21 @@ void __init e820__memory_setup_extended(u64 phys_addr, u32 data_len)
 void __init e820__register_nosave_regions(unsigned long limit_pfn)
 {
 	int i;
-	unsigned long pfn = 0;
+	u64 last_addr = 0;
 
 	for (i = 0; i < e820_table->nr_entries; i++) {
 		struct e820_entry *entry = &e820_table->entries[i];
 
-		if (pfn < PFN_UP(entry->addr))
-			register_nosave_region(pfn, PFN_UP(entry->addr));
-
-		pfn = PFN_DOWN(entry->addr + entry->size);
-
 		if (entry->type != E820_TYPE_RAM)
-			register_nosave_region(PFN_UP(entry->addr), pfn);
+			continue;
 
-		if (pfn >= limit_pfn)
-			break;
+		if (last_addr < entry->addr)
+			register_nosave_region(PFN_DOWN(last_addr), PFN_UP(entry->addr));
+
+		last_addr = entry->addr + entry->size;
 	}
+
+	register_nosave_region(PFN_DOWN(last_addr), limit_pfn);
 }
 
 #ifdef CONFIG_ACPI
@@ -1300,6 +1299,32 @@ void __init e820__memblock_setup(void)
 		memblock_add(entry->addr, entry->size);
 	}
 
+	/*
+	 * At this point memblock is only allowed to allocate from memory
+	 * below 1M (aka ISA_END_ADDRESS) up until direct map is completely set
+	 * up in init_mem_mapping().
+	 *
+	 * KHO kernels are special and use only scratch memory for memblock
+	 * allocations, but memory below 1M is ignored by kernel after early
+	 * boot and cannot be naturally marked as scratch.
+	 *
+	 * To allow allocation of the real-mode trampoline and a few (if any)
+	 * other very early allocations from below 1M forcibly mark the memory
+	 * below 1M as scratch.
+	 *
+	 * After real mode trampoline is allocated, we clear that scratch
+	 * marking.
+	 */
+	memblock_mark_kho_scratch(0, SZ_1M);
+
+	/*
+	 * 32-bit systems are limited to 4BG of memory even with HIGHMEM and
+	 * to even less without it.
+	 * Discard memory after max_pfn - the actual limit detected at runtime.
+	 */
+	if (IS_ENABLED(CONFIG_X86_32))
+		memblock_remove(PFN_PHYS(max_pfn), -1);
+
 	/* Throw away partial pages: */
 	memblock_trim_memory(PAGE_SIZE);