x86/mm: Make e820__end_ram_pfn() cover E820_TYPE_ACPI ranges

e820__end_of_ram_pfn() is used to calculate max_pfn which, among other things,
guides where direct mapping ends. Any memory above max_pfn is not going to be
present in the direct mapping.

e820__end_of_ram_pfn() finds the end of the RAM based on the highest
E820_TYPE_RAM range. But it doesn't includes E820_TYPE_ACPI ranges into
calculation.

Despite the name, E820_TYPE_ACPI covers not only ACPI data, but also EFI tables
and might be required by kernel to function properly.

Usually the problem is hidden because there is some E820_TYPE_RAM memory above
E820_TYPE_ACPI. But crashkernel only presents pre-allocated crash memory as
E820_TYPE_RAM on boot. If the pre-allocated range is small, it can fit under the
last E820_TYPE_ACPI range.

Modify e820__end_of_ram_pfn() and e820__end_of_low_ram_pfn() to cover
E820_TYPE_ACPI memory.

The problem was discovered during debugging kexec for TDX guest. TDX guest uses
E820_TYPE_ACPI to store the unaccepted memory bitmap and pass it between the
kernels on kexec.

Signed-off-by: Kirill A. Shutemov <[email protected]>
Signed-off-by: Borislav Petkov (AMD) <[email protected]>
Reviewed-by: Dave Hansen <[email protected]>
Tested-by: Tao Liu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: kiryl

arch/x86/kernel/e820.c

@@ -828,7 +828,7 @@ u64 __init e820__memblock_alloc_reserved(u64 size, u64 align)
 /*
  * Find the highest page frame number we have available
  */
-static unsigned long __init e820_end_pfn(unsigned long limit_pfn, enum e820_type type)
+static unsigned long __init e820__end_ram_pfn(unsigned long limit_pfn)
 {
 	int i;
 	unsigned long last_pfn = 0;
@@ -839,7 +839,8 @@ static unsigned long __init e820_end_pfn(unsigned long limit_pfn, enum e820_type
 		unsigned long start_pfn;
 		unsigned long end_pfn;
 
-		if (entry->type != type)
+		if (entry->type != E820_TYPE_RAM &&
+		    entry->type != E820_TYPE_ACPI)
 			continue;
 
 		start_pfn = entry->addr >> PAGE_SHIFT;
@@ -865,12 +866,12 @@ static unsigned long __init e820_end_pfn(unsigned long limit_pfn, enum e820_type
 
 unsigned long __init e820__end_of_ram_pfn(void)
 {
-	return e820_end_pfn(MAX_ARCH_PFN, E820_TYPE_RAM);
+	return e820__end_ram_pfn(MAX_ARCH_PFN);
 }
 
 unsigned long __init e820__end_of_low_ram_pfn(void)
 {
-	return e820_end_pfn(1UL << (32 - PAGE_SHIFT), E820_TYPE_RAM);
+	return e820__end_ram_pfn(1UL << (32 - PAGE_SHIFT));
 }
 
 static void __init early_panic(char *msg)