arch/x86/boot/compressed/idt_64.c

// SPDX-License-Identifier: GPL-2.0-only
#include <asm/trap_pf.h>
#include <asm/segment.h>
#include <asm/trapnr.h>
#include "misc.h"

static void set_idt_entry(int vector, void (*handler)(void))
{
	unsigned long address = (unsigned long)handler;
	gate_desc entry;

	memset(&entry, 0, sizeof(entry));

	entry.offset_low    = (u16)(address & 0xffff);
	entry.segment       = __KERNEL_CS;
	entry.bits.type     = GATE_TRAP;
	entry.bits.p        = 1;
	entry.offset_middle = (u16)((address >> 16) & 0xffff);
	entry.offset_high   = (u32)(address >> 32);

	memcpy(&boot_idt[vector], &entry, sizeof(entry));
}

/* Have this here so we don't need to include <asm/desc.h> */
static void load_boot_idt(const struct desc_ptr *dtr)
{
	asm volatile("lidt %0"::"m" (*dtr));
}

/* Setup IDT before kernel jumping to  .Lrelocated */
void load_stage1_idt(void)
{
	boot_idt_desc.address = (unsigned long)boot_idt;


	if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT))
		set_idt_entry(X86_TRAP_VC, boot_stage1_vc);

	load_boot_idt(&boot_idt_desc);
}

/*
 * Setup IDT after kernel jumping to  .Lrelocated.
 *
 * initialize_identity_maps() needs a #PF handler to be setup
 * in order to be able to fault-in identity mapping ranges; see
 * do_boot_page_fault().
 *
 * This #PF handler setup needs to happen in load_stage2_idt() where the
 * IDT is loaded and there the #VC IDT entry gets setup too.
 *
 * In order to be able to handle #VCs, one needs a GHCB which
 * gets setup with an already set up pagetable, which is done in
 * initialize_identity_maps(). And there's the catch 22: the boot #VC
 * handler do_boot_stage2_vc() needs to call early_setup_ghcb() itself
 * (and, especially set_page_decrypted()) because the SEV-ES setup code
 * cannot initialize a GHCB as there's no #PF handler yet...
 */
void load_stage2_idt(void)
{
	boot_idt_desc.address = (unsigned long)boot_idt;

	set_idt_entry(X86_TRAP_PF, boot_page_fault);

#ifdef CONFIG_AMD_MEM_ENCRYPT
	set_idt_entry(X86_TRAP_VC, boot_stage2_vc);
#endif

	load_boot_idt(&boot_idt_desc);
}

void cleanup_exception_handling(void)
{
	/*
	 * Flush GHCB from cache and map it encrypted again when running as
	 * SEV-ES guest.
	 */
	sev_es_shutdown_ghcb();

	/* Set a null-idt, disabling #PF and #VC handling */
	boot_idt_desc.size    = 0;
	boot_idt_desc.address = 0;
	load_boot_idt(&boot_idt_desc);
}