original_kernel/arch/x86/realmode/init.c

// SPDX-License-Identifier: GPL-2.0
#include <linux/io.h>
#include <linux/slab.h>
#include <linux/memblock.h>
#include <linux/cc_platform.h>
#include <linux/pgtable.h>

#include <asm/set_memory.h>
#include <asm/realmode.h>
#include <asm/tlbflush.h>
#include <asm/crash.h>
#include <asm/sev.h>

struct real_mode_header *real_mode_header;
u32 *trampoline_cr4_features;

/* Hold the pgd entry used on booting additional CPUs */
pgd_t trampoline_pgd_entry;

void load_trampoline_pgtable(void)
{
#ifdef CONFIG_X86_32
	load_cr3(initial_page_table);
#else
	/*
	 * This function is called before exiting to real-mode and that will
	 * fail with CR4.PCIDE still set.
	 */
	if (boot_cpu_has(X86_FEATURE_PCID))
		cr4_clear_bits(X86_CR4_PCIDE);

	write_cr3(real_mode_header->trampoline_pgd);
#endif

	/*
	 * The CR3 write above will not flush global TLB entries.
	 * Stale, global entries from previous page tables may still be
	 * present.  Flush those stale entries.
	 *
	 * This ensures that memory accessed while running with
	 * trampoline_pgd is *actually* mapped into trampoline_pgd.
	 */
	__flush_tlb_all();
}

void __init reserve_real_mode(void)
{
	phys_addr_t mem;
	size_t size = real_mode_size_needed();

	if (!size)
		return;

	WARN_ON(slab_is_available());

	/* Has to be under 1M so we can execute real-mode AP code. */
	mem = memblock_phys_alloc_range(size, PAGE_SIZE, 0, 1<<20);
	if (!mem)
		pr_info("No sub-1M memory is available for the trampoline\n");
	else
		set_real_mode_mem(mem);

	/*
	 * Unconditionally reserve the entire first 1M, see comment in
	 * setup_arch().
	 */
	memblock_reserve(0, SZ_1M);
}

static void __init sme_sev_setup_real_mode(struct trampoline_header *th)
{
#ifdef CONFIG_AMD_MEM_ENCRYPT
	if (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT))
		th->flags |= TH_FLAGS_SME_ACTIVE;

	if (cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT)) {
		/*
		 * Skip the call to verify_cpu() in secondary_startup_64 as it
		 * will cause #VC exceptions when the AP can't handle them yet.
		 */
		th->start = (u64) secondary_startup_64_no_verify;

		if (sev_es_setup_ap_jump_table(real_mode_header))
			panic("Failed to get/update SEV-ES AP Jump Table");
	}
#endif
}

static void __init setup_real_mode(void)
{
	u16 real_mode_seg;
	const u32 *rel;
	u32 count;
	unsigned char *base;
	unsigned long phys_base;
	struct trampoline_header *trampoline_header;
	size_t size = PAGE_ALIGN(real_mode_blob_end - real_mode_blob);
#ifdef CONFIG_X86_64
	u64 *trampoline_pgd;
	u64 efer;
	int i;
#endif

	base = (unsigned char *)real_mode_header;

	/*
	 * If SME is active, the trampoline area will need to be in
	 * decrypted memory in order to bring up other processors
	 * successfully. This is not needed for SEV.
	 */
	if (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT))
		set_memory_decrypted((unsigned long)base, size >> PAGE_SHIFT);

	memcpy(base, real_mode_blob, size);

	phys_base = __pa(base);
	real_mode_seg = phys_base >> 4;

	rel = (u32 *) real_mode_relocs;

	/* 16-bit segment relocations. */
	count = *rel++;
	while (count--) {
		u16 *seg = (u16 *) (base + *rel++);
		*seg = real_mode_seg;
	}

	/* 32-bit linear relocations. */
	count = *rel++;
	while (count--) {
		u32 *ptr = (u32 *) (base + *rel++);
		*ptr += phys_base;
	}

	/* Must be performed *after* relocation. */
	trampoline_header = (struct trampoline_header *)
		__va(real_mode_header->trampoline_header);

#ifdef CONFIG_X86_32
	trampoline_header->start = __pa_symbol(startup_32_smp);
	trampoline_header->gdt_limit = __BOOT_DS + 7;
	trampoline_header->gdt_base = __pa_symbol(boot_gdt);
#else
	/*
	 * Some AMD processors will #GP(0) if EFER.LMA is set in WRMSR
	 * so we need to mask it out.
	 */
	rdmsrl(MSR_EFER, efer);
	trampoline_header->efer = efer & ~EFER_LMA;

	trampoline_header->start = (u64) secondary_startup_64;
	trampoline_cr4_features = &trampoline_header->cr4;
	*trampoline_cr4_features = mmu_cr4_features;

	trampoline_header->flags = 0;

	trampoline_lock = &trampoline_header->lock;
	*trampoline_lock = 0;

	trampoline_pgd = (u64 *) __va(real_mode_header->trampoline_pgd);

	/* Map the real mode stub as virtual == physical */
	trampoline_pgd[0] = trampoline_pgd_entry.pgd;

	/*
	 * Include the entirety of the kernel mapping into the trampoline
	 * PGD.  This way, all mappings present in the normal kernel page
	 * tables are usable while running on trampoline_pgd.
	 */
	for (i = pgd_index(__PAGE_OFFSET); i < PTRS_PER_PGD; i++)
		trampoline_pgd[i] = init_top_pgt[i].pgd;
#endif

	sme_sev_setup_real_mode(trampoline_header);
}

/*
 * reserve_real_mode() gets called very early, to guarantee the
 * availability of low memory. This is before the proper kernel page
 * tables are set up, so we cannot set page permissions in that
 * function. Also trampoline code will be executed by APs so we
 * need to mark it executable at do_pre_smp_initcalls() at least,
 * thus run it as a early_initcall().
 */
static void __init set_real_mode_permissions(void)
{
	unsigned char *base = (unsigned char *) real_mode_header;
	size_t size = PAGE_ALIGN(real_mode_blob_end - real_mode_blob);

	size_t ro_size =
		PAGE_ALIGN(real_mode_header->ro_end) -
		__pa(base);

	size_t text_size =
		PAGE_ALIGN(real_mode_header->ro_end) -
		real_mode_header->text_start;

	unsigned long text_start =
		(unsigned long) __va(real_mode_header->text_start);

	set_memory_nx((unsigned long) base, size >> PAGE_SHIFT);
	set_memory_ro((unsigned long) base, ro_size >> PAGE_SHIFT);
	set_memory_x((unsigned long) text_start, text_size >> PAGE_SHIFT);
}

void __init init_real_mode(void)
{
	if (!real_mode_header)
		panic("Real mode trampoline was not allocated");

	setup_real_mode();
	set_real_mode_permissions();
}

static int __init do_init_real_mode(void)
{
	x86_platform.realmode_init();
	return 0;
}
early_initcall(do_init_real_mode);