x86/boot/e820: Simplify append_e820_table() and remove restriction on single-entry tables

So append_e820_table() begins with this weird condition that checks 'nr_entries':

    static int __init append_e820_table(struct boot_e820_entry *entries, u32 nr_entries)
    {
            /* Only one memory region (or negative)? Ignore it */
            if (nr_entries < 2)
                    return -1;

Firstly, 'nr_entries' has been an u32 since 2017 and cannot be negative.

Secondly, there's nothing inherently wrong with single-entry E820 maps,
especially in virtualized environments.

So remove this restriction and remove the __append_e820_table()
indirection.

Also:

 - fix/update comments
 - remove obsolete comments

This shrinks the generated code a bit as well:

   text       data        bss        dec        hex    filename
   7549      44072          0      51621       c9a5    e820.o.before
   7533      44072          0      51605       c995    e820.o.after

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Shevchenko <andy@kernel.org>
Cc: Arnd Bergmann <arnd@kernel.org>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: H . Peter Anvin <hpa@zytor.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Paul Menzel <pmenzel@molgen.mpg.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20250515120549.2820541-26-mingo@kernel.org

Author: ingomolnar

arch/x86/kernel/e820.c

@@ -441,17 +441,22 @@ __init int e820__update_table(struct e820_table *table)
 	return 0;
 }
 
-__init static int __append_e820_table(struct boot_e820_entry *entries, u32 nr_entries)
+/*
+ * Copy the BIOS E820 map into the kernel's e820_table.
+ *
+ * Sanity-check it while we're at it..
+ */
+__init static int append_e820_table(struct boot_e820_entry *entries, u32 nr_entries)
 {
 	struct boot_e820_entry *entry = entries;
 
 	while (nr_entries) {
 		u64 start = entry->addr;
-		u64 size = entry->size;
-		u64 end = start + size - 1;
-		u32 type = entry->type;
+		u64 size  = entry->size;
+		u64 end   = start + size-1;
+		u32 type  = entry->type;
 
-		/* Ignore the entry on 64-bit overflow: */
+		/* Ignore the remaining entries on 64-bit overflow: */
 		if (start > end && likely(size))
 			return -1;
 
@@ -463,24 +468,6 @@ __init static int __append_e820_table(struct boot_e820_entry *entries, u32 nr_en
 	return 0;
 }
 
-/*
- * Copy the BIOS E820 map into a safe place.
- *
- * Sanity-check it while we're at it..
- *
- * If we're lucky and live on a modern system, the setup code
- * will have given us a memory map that we can use to properly
- * set up memory.  If we aren't, we'll fake a memory map.
- */
-__init static int append_e820_table(struct boot_e820_entry *entries, u32 nr_entries)
-{
-	/* Only one memory region (or negative)? Ignore it */
-	if (nr_entries < 2)
-		return -1;
-
-	return __append_e820_table(entries, nr_entries);
-}
-
 __init static u64
 __e820__range_update(struct e820_table *table, u64 start, u64 size, enum e820_type old_type, enum e820_type new_type)
 {
@@ -754,7 +741,7 @@ __init void e820__memory_setup_extended(u64 phys_addr, u32 data_len)
 	entries = sdata->len / sizeof(*extmap);
 	extmap = (struct boot_e820_entry *)(sdata->data);
 
-	__append_e820_table(extmap, entries);
+	append_e820_table(extmap, entries);
 	e820__update_table(e820_table);
 
 	memcpy(e820_table_kexec, e820_table, sizeof(*e820_table_kexec));