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From: Vegard Nossum <vegard.nossum@oracle.com>
To: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org,
        Brian Gerst <brgerst@gmail.com>, Peter Zijlstra <peterz@infradead.org>,
        Linus Torvalds <torvalds@linuxfoundation.org>,
        Vegard Nossum <vegard.nossum@oracle.com>
Subject: [PATCH 2/5] x86: replace magic numbers in GDT descriptors, part 1
Date: Tue, 19 Dec 2023 16:11:57 +0100
Message-Id: <20231219151200.2878271-3-vegard.nossum@oracle.com>
In-Reply-To: <20231219151200.2878271-1-vegard.nossum@oracle.com>
References: <20231219151200.2878271-1-vegard.nossum@oracle.com>
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We'd like to replace all the magic numbers in various GDT descriptors
with new, semantically meaningful, symbolic values.

In order to be able to verify that the change doesn't cause any actual
changes to the compiled binary code, I've split the change into two
patches:

Part 1 (this commit): everything _but_ actually replacing the numbers
Part 2 (the following commit): _only_ replacing the numbers

These two commits may be squashed together when merged.

The reason we need this split for verification is that including new
headers causes some spurious changes to the object files, mostly line
number changes in the debug info but occasionally other subtle codegen
changes.

Link: https://lore.kernel.org/all/CAHk-=wib5XLebuEra7y2YH96wxdk=8vJnA8XoVq0FExpzVvN=Q@mail.gmail.com/
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
---
 arch/x86/boot/pm.c               | 1 +
 arch/x86/include/asm/desc_defs.h | 2 ++
 arch/x86/kernel/cpu/common.c     | 8 --------
 arch/x86/platform/pvh/head.S     | 1 +
 arch/x86/realmode/rm/reboot.S    | 1 +
 5 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/arch/x86/boot/pm.c b/arch/x86/boot/pm.c
index 40031a614712..0361b5307bd8 100644
--- a/arch/x86/boot/pm.c
+++ b/arch/x86/boot/pm.c
@@ -11,6 +11,7 @@
  */
 
 #include "boot.h"
+#include <asm/desc_defs.h>
 #include <asm/segment.h>
 
 /*
diff --git a/arch/x86/include/asm/desc_defs.h b/arch/x86/include/asm/desc_defs.h
index b33f5bb240eb..014878e584fe 100644
--- a/arch/x86/include/asm/desc_defs.h
+++ b/arch/x86/include/asm/desc_defs.h
@@ -144,6 +144,7 @@ struct gate_struct {
 
 typedef struct gate_struct gate_desc;
 
+#ifndef _SETUP
 static inline unsigned long gate_offset(const gate_desc *g)
 {
 #ifdef CONFIG_X86_64
@@ -158,6 +159,7 @@ static inline unsigned long gate_segment(const gate_desc *g)
 {
 	return g->segment;
 }
+#endif
 
 struct desc_ptr {
 	unsigned short size;
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index b14fc8c1c953..ceb6e4b6d57e 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -204,25 +204,17 @@ DEFINE_PER_CPU_PAGE_ALIGNED(struct gdt_page, gdt_page) = { .gdt = {
 	 * They code segments and data segments have fixed 64k limits,
 	 * the transfer segment sizes are set at run time.
 	 */
-	/* 32-bit code */
 	[GDT_ENTRY_PNPBIOS_CS32]	= GDT_ENTRY_INIT(0x409a, 0, 0xffff),
-	/* 16-bit code */
 	[GDT_ENTRY_PNPBIOS_CS16]	= GDT_ENTRY_INIT(0x009a, 0, 0xffff),
-	/* 16-bit data */
 	[GDT_ENTRY_PNPBIOS_DS]		= GDT_ENTRY_INIT(0x0092, 0, 0xffff),
-	/* 16-bit data */
 	[GDT_ENTRY_PNPBIOS_TS1]		= GDT_ENTRY_INIT(0x0092, 0, 0),
-	/* 16-bit data */
 	[GDT_ENTRY_PNPBIOS_TS2]		= GDT_ENTRY_INIT(0x0092, 0, 0),
 	/*
 	 * The APM segments have byte granularity and their bases
 	 * are set at run time.  All have 64k limits.
 	 */
-	/* 32-bit code */
 	[GDT_ENTRY_APMBIOS_BASE]	= GDT_ENTRY_INIT(0x409a, 0, 0xffff),
-	/* 16-bit code */
 	[GDT_ENTRY_APMBIOS_BASE+1]	= GDT_ENTRY_INIT(0x009a, 0, 0xffff),
-	/* data */
 	[GDT_ENTRY_APMBIOS_BASE+2]	= GDT_ENTRY_INIT(0x4092, 0, 0xffff),
 
 	[GDT_ENTRY_ESPFIX_SS]		= GDT_ENTRY_INIT(0xc092, 0, 0xfffff),
diff --git a/arch/x86/platform/pvh/head.S b/arch/x86/platform/pvh/head.S
index c4365a05ab83..9bcafdded2a1 100644
--- a/arch/x86/platform/pvh/head.S
+++ b/arch/x86/platform/pvh/head.S
@@ -11,6 +11,7 @@
 #include <linux/elfnote.h>
 #include <linux/init.h>
 #include <linux/linkage.h>
+#include <asm/desc_defs.h>
 #include <asm/segment.h>
 #include <asm/asm.h>
 #include <asm/boot.h>
diff --git a/arch/x86/realmode/rm/reboot.S b/arch/x86/realmode/rm/reboot.S
index f10515b10e0a..447641820a8d 100644
--- a/arch/x86/realmode/rm/reboot.S
+++ b/arch/x86/realmode/rm/reboot.S
@@ -1,5 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 #include <linux/linkage.h>
+#include <asm/desc_defs.h>
 #include <asm/segment.h>
 #include <asm/page_types.h>
 #include <asm/processor-flags.h>
-- 
2.34.1