linux-kernel - [PATCH 25/29] x86/boot/e820: Simplify append_e820_table() and remove restriction on single-entry tables

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Message-ID: <20250421185210.3372306-26-mingo@kernel.org>
Date: Mon, 21 Apr 2025 20:52:05 +0200
From: Ingo Molnar <mingo@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: Andy Shevchenko <andy@...nel.org>,
	Arnd Bergmann <arnd@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Juergen Gross <jgross@...e.com>,
	"H . Peter Anvin" <hpa@...or.com>,
	Kees Cook <keescook@...omium.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mike Rapoport <rppt@...nel.org>,
	Paul Menzel <pmenzel@...gen.mpg.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	David Woodhouse <dwmw@...zon.co.uk>
Subject: [PATCH 25/29] 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@...nel.org>
Cc: Andy Shevchenko <andy@...nel.org>
Cc: Arnd Bergmann <arnd@...nel.org>
Cc: David Woodhouse <dwmw@...zon.co.uk>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mike Rapoport (Microsoft) <rppt@...nel.org>
---
 arch/x86/kernel/e820.c | 35 +++++++++++------------------------
 1 file changed, 11 insertions(+), 24 deletions(-)

diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index ec5628a844dc..27bc45a65807 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -483,17 +483,22 @@ __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;
 
@@ -505,24 +510,6 @@ __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)
 {
@@ -796,7 +783,7 @@ __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));
-- 
2.45.2