linux-kernel - [PATCH v2 07/17] x86/head64: Simplify GDT/IDT initialization code

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Message-ID: <20240125112818.2016733-26-ardb+git@google.com>
Date: Thu, 25 Jan 2024 12:28:26 +0100
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: Ard Biesheuvel <ardb@...nel.org>, Kevin Loughlin <kevinloughlin@...gle.com>, 
	Tom Lendacky <thomas.lendacky@....com>, Dionna Glaze <dionnaglaze@...gle.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, Andy Lutomirski <luto@...nel.org>, 
	Arnd Bergmann <arnd@...db.de>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
	Brian Gerst <brgerst@...il.com>, linux-arch@...r.kernel.org, llvm@...ts.linux.dev
Subject: [PATCH v2 07/17] x86/head64: Simplify GDT/IDT initialization code

From: Ard Biesheuvel <ardb@...nel.org>

There used to be two separate code paths for programming the IDT early:
one that was called via the 1:1 mapping, and one via the kernel virtual
mapping, where the former used explicit pointer fixups to obtain 1:1
mapped addresses.

That distinction is now gone so the GDT/IDT init code can be unified and
simplified accordingly.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/kernel/head64.c | 59 +++++++-------------
 1 file changed, 19 insertions(+), 40 deletions(-)

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index a4a380494703..993d888a3172 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -59,21 +59,12 @@ EXPORT_SYMBOL(vmemmap_base);
 /*
  * GDT used on the boot CPU before switching to virtual addresses.
  */
-static struct desc_struct startup_gdt[GDT_ENTRIES] __initdata = {
+static struct desc_struct startup_gdt[GDT_ENTRIES] __initconst = {
 	[GDT_ENTRY_KERNEL32_CS]         = GDT_ENTRY_INIT(DESC_CODE32, 0, 0xfffff),
 	[GDT_ENTRY_KERNEL_CS]           = GDT_ENTRY_INIT(DESC_CODE64, 0, 0xfffff),
 	[GDT_ENTRY_KERNEL_DS]           = GDT_ENTRY_INIT(DESC_DATA64, 0, 0xfffff),
 };
 
-/*
- * Address needs to be set at runtime because it references the startup_gdt
- * while the kernel still uses a direct mapping.
- */
-static struct desc_ptr startup_gdt_descr __initdata = {
-	.size = sizeof(startup_gdt)-1,
-	.address = 0,
-};
-
 #define __va_symbol(sym) ({						\
 	unsigned long __v;						\
 	asm("movq $" __stringify(sym) ", %0":"=r"(__v));		\
@@ -363,7 +354,7 @@ void __init do_early_exception(struct pt_regs *regs, int trapnr)
 	early_fixup_exception(regs, trapnr);
 }
 
-/* Don't add a printk in there. printk relies on the PDA which is not initialized 
+/* Don't add a printk in there. printk relies on the PDA which is not initialized
    yet. */
 void __init clear_bss(void)
 {
@@ -517,47 +508,32 @@ void __init __noreturn x86_64_start_reservations(char *real_mode_data)
  */
 static gate_desc bringup_idt_table[NUM_EXCEPTION_VECTORS] __page_aligned_data;
 
-static struct desc_ptr bringup_idt_descr = {
-	.size		= (NUM_EXCEPTION_VECTORS * sizeof(gate_desc)) - 1,
-	.address	= 0, /* Set at runtime */
-};
-
-static void set_bringup_idt_handler(gate_desc *idt, int n, void *handler)
-{
-#ifdef CONFIG_AMD_MEM_ENCRYPT
-	struct idt_data data;
-	gate_desc desc;
-
-	init_idt_data(&data, n, handler);
-	idt_init_desc(&desc, &data);
-	native_write_idt_entry(idt, n, &desc);
-#endif
-}
-
-/* This runs while still in the direct mapping */
-static void __head startup_64_load_idt(void)
+static void early_load_idt(void (*handler)(void))
 {
 	gate_desc *idt = bringup_idt_table;
+	struct desc_ptr bringup_idt_descr;
+
+	if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT)) {
+		struct idt_data data;
+		gate_desc desc;
 
-	if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT))
 		/* VMM Communication Exception */
-		set_bringup_idt_handler(idt, X86_TRAP_VC, vc_no_ghcb);
+		init_idt_data(&data, X86_TRAP_VC, handler);
+		idt_init_desc(&desc, &data);
+		native_write_idt_entry(idt, X86_TRAP_VC, &desc);
+	}
 
 	bringup_idt_descr.address = (unsigned long)idt;
+	bringup_idt_descr.size = sizeof(bringup_idt_table);
 	native_load_idt(&bringup_idt_descr);
 }
 
-/* This is used when running on kernel addresses */
 void early_setup_idt(void)
 {
-	/* VMM Communication Exception */
-	if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT)) {
+	if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT))
 		setup_ghcb();
-		set_bringup_idt_handler(bringup_idt_table, X86_TRAP_VC, vc_boot_ghcb);
-	}
 
-	bringup_idt_descr.address = (unsigned long)bringup_idt_table;
-	native_load_idt(&bringup_idt_descr);
+	early_load_idt(vc_boot_ghcb);
 }
 
 /*
@@ -565,8 +541,11 @@ void early_setup_idt(void)
  */
 void __head startup_64_setup_env(void)
 {
+	struct desc_ptr startup_gdt_descr;
+
 	/* Load GDT */
 	startup_gdt_descr.address = (unsigned long)startup_gdt;
+	startup_gdt_descr.size = sizeof(startup_gdt) - 1;
 	native_load_gdt(&startup_gdt_descr);
 
 	/* New GDT is live - reload data segment registers */
@@ -574,5 +553,5 @@ void __head startup_64_setup_env(void)
 		     "movl %%eax, %%ss\n"
 		     "movl %%eax, %%es\n" : : "a"(__KERNEL_DS) : "memory");
 
-	startup_64_load_idt();
+	early_load_idt(vc_no_ghcb);
 }
-- 
2.43.0.429.g432eaa2c6b-goog