[PATCH v3 09/19] x86/head64: Simplify GDT/IDT initialization code

Ard Biesheuvel
2024-01-29T18:05:51Z

From: Ard Biesheuvel <ardb@kernel.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@kernel.org>
---
arch/x86/kernel/head64.c | 57 +++++++-------------
1 file changed, 18 insertions(+), 39 deletions(-)

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index a4a380494703..58c58c66dec9 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)); \
@@ -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