linux/arch/x86/include/asm/cpu_entry_area.h

// SPDX-License-Identifier: GPL-2.0

#ifndef _ASM_X86_CPU_ENTRY_AREA_H
#define _ASM_X86_CPU_ENTRY_AREA_H

#include <linux/percpu-defs.h>
#include <asm/processor.h>

/*
 * cpu_entry_area is a percpu region that contains things needed by the CPU
 * and early entry/exit code.  Real types aren't used for all fields here
 * to avoid circular header dependencies.
 *
 * Every field is a virtual alias of some other allocated backing store.
 * There is no direct allocation of a struct cpu_entry_area.
 */
struct cpu_entry_area {
	char gdt[PAGE_SIZE];

	/*
	 * The GDT is just below entry_stack and thus serves (on x86_64) as
	 * a a read-only guard page.
	 */
	struct entry_stack_page entry_stack_page;

	/*
	 * On x86_64, the TSS is mapped RO.  On x86_32, it's mapped RW because
	 * we need task switches to work, and task switches write to the TSS.
	 */
	struct tss_struct tss;

	char entry_trampoline[PAGE_SIZE];

#ifdef CONFIG_X86_64
	/*
	 * Exception stacks used for IST entries.
	 *
	 * In the future, this should have a separate slot for each stack
	 * with guard pages between them.
	 */
	char exception_stacks[(N_EXCEPTION_STACKS - 1) * EXCEPTION_STKSZ + DEBUG_STKSZ];
#endif
};

#define CPU_ENTRY_AREA_SIZE	(sizeof(struct cpu_entry_area))
#define CPU_ENTRY_AREA_PAGES	(CPU_ENTRY_AREA_SIZE / PAGE_SIZE)

DECLARE_PER_CPU(struct cpu_entry_area *, cpu_entry_area);

extern void setup_cpu_entry_areas(void);

#endif