WSL2-Linux-Kernel/arch/x86/kernel/head64.c

/*
 *  prepare to run common code
 *
 *  Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
 */

#include <linux/init.h>
#include <linux/linkage.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/percpu.h>
#include <linux/start_kernel.h>

#include <asm/processor.h>
#include <asm/proto.h>
#include <asm/smp.h>
#include <asm/setup.h>
#include <asm/desc.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>
#include <asm/sections.h>
#include <asm/kdebug.h>
#include <asm/e820.h>

static void __init zap_identity_mappings(void)
{
	pgd_t *pgd = pgd_offset_k(0UL);
	pgd_clear(pgd);
	__flush_tlb_all();
}

/* Don't add a printk in there. printk relies on the PDA which is not initialized 
   yet. */
static void __init clear_bss(void)
{
	memset(__bss_start, 0,
	       (unsigned long) __bss_stop - (unsigned long) __bss_start);
}

static void __init copy_bootdata(char *real_mode_data)
{
	char * command_line;

	memcpy(&boot_params, real_mode_data, sizeof boot_params);
	if (boot_params.hdr.cmd_line_ptr) {
		command_line = __va(boot_params.hdr.cmd_line_ptr);
		memcpy(boot_command_line, command_line, COMMAND_LINE_SIZE);
	}
}

#define BIOS_EBDA_SEGMENT 0x40E
#define BIOS_LOWMEM_KILOBYTES 0x413

/*
 * The BIOS places the EBDA/XBDA at the top of conventional
 * memory, and usually decreases the reported amount of
 * conventional memory (int 0x12) too. This also contains a
 * workaround for Dell systems that neglect to reserve EBDA.
 * The same workaround also avoids a problem with the AMD768MPX
 * chipset: reserve a page before VGA to prevent PCI prefetch
 * into it (errata #56). Usually the page is reserved anyways,
 * unless you have no PS/2 mouse plugged in.
 */
static void __init reserve_ebda_region(void)
{
	unsigned int lowmem, ebda_addr;

	/* To determine the position of the EBDA and the */
	/* end of conventional memory, we need to look at */
	/* the BIOS data area. In a paravirtual environment */
	/* that area is absent. We'll just have to assume */
	/* that the paravirt case can handle memory setup */
	/* correctly, without our help. */
	if (paravirt_enabled())
		return;

	/* end of low (conventional) memory */
	lowmem = *(unsigned short *)__va(BIOS_LOWMEM_KILOBYTES);
	lowmem <<= 10;

	/* start of EBDA area */
	ebda_addr = *(unsigned short *)__va(BIOS_EBDA_SEGMENT);
	ebda_addr <<= 4;

	/* Fixup: bios puts an EBDA in the top 64K segment */
	/* of conventional memory, but does not adjust lowmem. */
	if ((lowmem - ebda_addr) <= 0x10000)
		lowmem = ebda_addr;

	/* Fixup: bios does not report an EBDA at all. */
	/* Some old Dells seem to need 4k anyhow (bugzilla 2990) */
	if ((ebda_addr == 0) && (lowmem >= 0x9f000))
		lowmem = 0x9f000;

	/* Paranoia: should never happen, but... */
	if ((lowmem == 0) || (lowmem >= 0x100000))
		lowmem = 0x9f000;

	/* reserve all memory between lowmem and the 1MB mark */
	reserve_early(lowmem, 0x100000, "BIOS reserved");
}

void __init x86_64_start_kernel(char * real_mode_data)
{
	int i;

	/*
	 * Build-time sanity checks on the kernel image and module
	 * area mappings. (these are purely build-time and produce no code)
	 */
	BUILD_BUG_ON(MODULES_VADDR < KERNEL_IMAGE_START);
	BUILD_BUG_ON(MODULES_VADDR-KERNEL_IMAGE_START < KERNEL_IMAGE_SIZE);
	BUILD_BUG_ON(MODULES_LEN + KERNEL_IMAGE_SIZE > 2*PUD_SIZE);
	BUILD_BUG_ON((KERNEL_IMAGE_START & ~PMD_MASK) != 0);
	BUILD_BUG_ON((MODULES_VADDR & ~PMD_MASK) != 0);
	BUILD_BUG_ON(!(MODULES_VADDR > __START_KERNEL));
	BUILD_BUG_ON(!(((MODULES_END - 1) & PGDIR_MASK) ==
				(__START_KERNEL & PGDIR_MASK)));

	/* clear bss before set_intr_gate with early_idt_handler */
	clear_bss();

	/* Make NULL pointers segfault */
	zap_identity_mappings();

	/* Cleanup the over mapped high alias */
	cleanup_highmap();

	for (i = 0; i < NUM_EXCEPTION_VECTORS; i++) {
#ifdef CONFIG_EARLY_PRINTK
		set_intr_gate(i, &early_idt_handlers[i]);
#else
		set_intr_gate(i, early_idt_handler);
#endif
	}
	load_idt((const struct desc_ptr *)&idt_descr);

	early_printk("Kernel alive\n");

 	for (i = 0; i < NR_CPUS; i++)
 		cpu_pda(i) = &boot_cpu_pda[i];

	pda_init(0);
	copy_bootdata(__va(real_mode_data));

	reserve_early(__pa_symbol(&_text), __pa_symbol(&_end), "TEXT DATA BSS");

	/* Reserve INITRD */
	if (boot_params.hdr.type_of_loader && boot_params.hdr.ramdisk_image) {
		unsigned long ramdisk_image = boot_params.hdr.ramdisk_image;
		unsigned long ramdisk_size  = boot_params.hdr.ramdisk_size;
		unsigned long ramdisk_end   = ramdisk_image + ramdisk_size;
		reserve_early(ramdisk_image, ramdisk_end, "RAMDISK");
	}

	reserve_ebda_region();

	/*
	 * At this point everything still needed from the boot loader
	 * or BIOS or kernel text should be early reserved or marked not
	 * RAM in e820. All other memory is free game.
	 */

	start_kernel();
}