Linux 6.14-rc1

[linux.git] / arch / s390 / boot / startup.c

// SPDX-License-Identifier: GPL-2.0
#define boot_fmt(fmt) "startup: " fmt
#include <linux/string.h>
#include <linux/elf.h>
#include <asm/page-states.h>
#include <asm/boot_data.h>
#include <asm/extmem.h>
#include <asm/sections.h>
#include <asm/maccess.h>
#include <asm/cpu_mf.h>
#include <asm/setup.h>
#include <asm/kasan.h>
#include <asm/kexec.h>
#include <asm/sclp.h>
#include <asm/diag.h>
#include <asm/uv.h>
#include <asm/abs_lowcore.h>
#include <asm/physmem_info.h>
#include "decompressor.h"
#include "boot.h"
#include "uv.h"

struct vm_layout __bootdata_preserved(vm_layout);
unsigned long __bootdata_preserved(__abs_lowcore);
unsigned long __bootdata_preserved(__memcpy_real_area);
pte_t *__bootdata_preserved(memcpy_real_ptep);
unsigned long __bootdata_preserved(VMALLOC_START);
unsigned long __bootdata_preserved(VMALLOC_END);
struct page *__bootdata_preserved(vmemmap);
unsigned long __bootdata_preserved(vmemmap_size);
unsigned long __bootdata_preserved(MODULES_VADDR);
unsigned long __bootdata_preserved(MODULES_END);
unsigned long __bootdata_preserved(max_mappable);
unsigned long __bootdata_preserved(page_noexec_mask);
unsigned long __bootdata_preserved(segment_noexec_mask);
unsigned long __bootdata_preserved(region_noexec_mask);
int __bootdata_preserved(relocate_lowcore);

u64 __bootdata_preserved(stfle_fac_list[16]);
struct oldmem_data __bootdata_preserved(oldmem_data);

struct machine_info machine;

void error(char *x)
{
        boot_emerg("%s\n", x);
        boot_emerg(" -- System halted\n");
        disabled_wait();
}

static void detect_facilities(void)
{
        if (test_facility(8)) {
                machine.has_edat1 = 1;
                local_ctl_set_bit(0, CR0_EDAT_BIT);
        }
        if (test_facility(78))
                machine.has_edat2 = 1;
        page_noexec_mask = -1UL;
        segment_noexec_mask = -1UL;
        region_noexec_mask = -1UL;
        if (!test_facility(130)) {
                page_noexec_mask &= ~_PAGE_NOEXEC;
                segment_noexec_mask &= ~_SEGMENT_ENTRY_NOEXEC;
                region_noexec_mask &= ~_REGION_ENTRY_NOEXEC;
        }
}

static int cmma_test_essa(void)
{
        unsigned long reg1, reg2, tmp = 0;
        int rc = 1;
        psw_t old;

        /* Test ESSA_GET_STATE */
        asm volatile(
                "       mvc     0(16,%[psw_old]),0(%[psw_pgm])\n"
                "       epsw    %[reg1],%[reg2]\n"
                "       st      %[reg1],0(%[psw_pgm])\n"
                "       st      %[reg2],4(%[psw_pgm])\n"
                "       larl    %[reg1],1f\n"
                "       stg     %[reg1],8(%[psw_pgm])\n"
                "       .insn   rrf,0xb9ab0000,%[tmp],%[tmp],%[cmd],0\n"
                "       la      %[rc],0\n"
                "1:     mvc     0(16,%[psw_pgm]),0(%[psw_old])\n"
                : [reg1] "=&d" (reg1),
                  [reg2] "=&a" (reg2),
                  [rc] "+&d" (rc),
                  [tmp] "=&d" (tmp),
                  "+Q" (get_lowcore()->program_new_psw),
                  "=Q" (old)
                : [psw_old] "a" (&old),
                  [psw_pgm] "a" (&get_lowcore()->program_new_psw),
                  [cmd] "i" (ESSA_GET_STATE)
                : "cc", "memory");
        return rc;
}

static void cmma_init(void)
{
        if (!cmma_flag)
                return;
        if (cmma_test_essa()) {
                cmma_flag = 0;
                return;
        }
        if (test_facility(147))
                cmma_flag = 2;
}

static void setup_lpp(void)
{
        get_lowcore()->current_pid = 0;
        get_lowcore()->lpp = LPP_MAGIC;
        if (test_facility(40))
                lpp(&get_lowcore()->lpp);
}

#ifdef CONFIG_KERNEL_UNCOMPRESSED
static unsigned long mem_safe_offset(void)
{
        return (unsigned long)_compressed_start;
}

static void deploy_kernel(void *output)
{
        void *uncompressed_start = (void *)_compressed_start;

        if (output == uncompressed_start)
                return;
        memmove(output, uncompressed_start, vmlinux.image_size);
        memset(uncompressed_start, 0, vmlinux.image_size);
}
#endif

static void rescue_initrd(unsigned long min, unsigned long max)
{
        unsigned long old_addr, addr, size;

        if (!IS_ENABLED(CONFIG_BLK_DEV_INITRD))
                return;
        if (!get_physmem_reserved(RR_INITRD, &addr, &size))
                return;
        if (addr >= min && addr + size <= max)
                return;
        old_addr = addr;
        physmem_free(RR_INITRD);
        addr = physmem_alloc_or_die(RR_INITRD, size, 0);
        memmove((void *)addr, (void *)old_addr, size);
}

static void copy_bootdata(void)
{
        if (__boot_data_end - __boot_data_start != vmlinux.bootdata_size)
                error(".boot.data section size mismatch");
        memcpy((void *)vmlinux.bootdata_off, __boot_data_start, vmlinux.bootdata_size);
        if (__boot_data_preserved_end - __boot_data_preserved_start != vmlinux.bootdata_preserved_size)
                error(".boot.preserved.data section size mismatch");
        memcpy((void *)vmlinux.bootdata_preserved_off, __boot_data_preserved_start, vmlinux.bootdata_preserved_size);
}

static void kaslr_adjust_relocs(unsigned long min_addr, unsigned long max_addr,
                                unsigned long offset, unsigned long phys_offset)
{
        int *reloc;
        long loc;

        /* Adjust R_390_64 relocations */
        for (reloc = (int *)__vmlinux_relocs_64_start; reloc < (int *)__vmlinux_relocs_64_end; reloc++) {
                loc = (long)*reloc + phys_offset;
                if (loc < min_addr || loc > max_addr)
                        error("64-bit relocation outside of kernel!\n");
                *(u64 *)loc += offset;
        }
}

static void kaslr_adjust_got(unsigned long offset)
{
        u64 *entry;

        /*
         * Adjust GOT entries, except for ones for undefined weak symbols
         * that resolved to zero. This also skips the first three reserved
         * entries on s390x that are zero.
         */
        for (entry = (u64 *)vmlinux.got_start; entry < (u64 *)vmlinux.got_end; entry++) {
                if (*entry)
                        *entry += offset;
        }
}

/*
 * Merge information from several sources into a single ident_map_size value.
 * "ident_map_size" represents the upper limit of physical memory we may ever
 * reach. It might not be all online memory, but also include standby (offline)
 * memory or memory areas reserved for other means (e.g., memory devices such as
 * virtio-mem).
 *
 * "ident_map_size" could be lower then actual standby/reserved or even online
 * memory present, due to limiting factors. We should never go above this limit.
 * It is the size of our identity mapping.
 *
 * Consider the following factors:
 * 1. max_physmem_end - end of physical memory online, standby or reserved.
 *    Always >= end of the last online memory range (get_physmem_online_end()).
 * 2. CONFIG_MAX_PHYSMEM_BITS - the maximum size of physical memory the
 *    kernel is able to support.
 * 3. "mem=" kernel command line option which limits physical memory usage.
 * 4. OLDMEM_BASE which is a kdump memory limit when the kernel is executed as
 *    crash kernel.
 * 5. "hsa" size which is a memory limit when the kernel is executed during
 *    zfcp/nvme dump.
 */
static void setup_ident_map_size(unsigned long max_physmem_end)
{
        unsigned long hsa_size;

        ident_map_size = max_physmem_end;
        if (memory_limit)
                ident_map_size = min(ident_map_size, memory_limit);
        ident_map_size = min(ident_map_size, 1UL << MAX_PHYSMEM_BITS);

#ifdef CONFIG_CRASH_DUMP
        if (oldmem_data.start) {
                __kaslr_enabled = 0;
                ident_map_size = min(ident_map_size, oldmem_data.size);
                boot_debug("kdump memory limit:  0x%016lx\n", oldmem_data.size);
        } else if (ipl_block_valid && is_ipl_block_dump()) {
                __kaslr_enabled = 0;
                if (!sclp_early_get_hsa_size(&hsa_size) && hsa_size) {
                        ident_map_size = min(ident_map_size, hsa_size);
                        boot_debug("Stand-alone dump limit: 0x%016lx\n", hsa_size);
                }
        }
#endif
        boot_debug("Identity map size:   0x%016lx\n", ident_map_size);
}

#define FIXMAP_SIZE     round_up(MEMCPY_REAL_SIZE + ABS_LOWCORE_MAP_SIZE, sizeof(struct lowcore))

static unsigned long get_vmem_size(unsigned long identity_size,
                                   unsigned long vmemmap_size,
                                   unsigned long vmalloc_size,
                                   unsigned long rte_size)
{
        unsigned long max_mappable, vsize;

        max_mappable = max(identity_size, MAX_DCSS_ADDR);
        vsize = round_up(SZ_2G + max_mappable, rte_size) +
                round_up(vmemmap_size, rte_size) +
                FIXMAP_SIZE + MODULES_LEN + KASLR_LEN;
        if (IS_ENABLED(CONFIG_KMSAN))
                vsize += MODULES_LEN * 2;
        return size_add(vsize, vmalloc_size);
}

static unsigned long setup_kernel_memory_layout(unsigned long kernel_size)
{
        unsigned long vmemmap_start;
        unsigned long kernel_start;
        unsigned long asce_limit;
        unsigned long rte_size;
        unsigned long pages;
        unsigned long vsize;
        unsigned long vmax;

        pages = ident_map_size / PAGE_SIZE;
        /* vmemmap contains a multiple of PAGES_PER_SECTION struct pages */
        vmemmap_size = SECTION_ALIGN_UP(pages) * sizeof(struct page);

        /* choose kernel address space layout: 4 or 3 levels. */
        BUILD_BUG_ON(!IS_ALIGNED(TEXT_OFFSET, THREAD_SIZE));
        BUILD_BUG_ON(!IS_ALIGNED(__NO_KASLR_START_KERNEL, THREAD_SIZE));
        BUILD_BUG_ON(__NO_KASLR_END_KERNEL > _REGION1_SIZE);
        vsize = get_vmem_size(ident_map_size, vmemmap_size, vmalloc_size, _REGION3_SIZE);
        boot_debug("vmem size estimated: 0x%016lx\n", vsize);
        if (IS_ENABLED(CONFIG_KASAN) || __NO_KASLR_END_KERNEL > _REGION2_SIZE ||
            (vsize > _REGION2_SIZE && kaslr_enabled())) {
                asce_limit = _REGION1_SIZE;
                if (__NO_KASLR_END_KERNEL > _REGION2_SIZE) {
                        rte_size = _REGION2_SIZE;
                        vsize = get_vmem_size(ident_map_size, vmemmap_size, vmalloc_size, _REGION2_SIZE);
                } else {
                        rte_size = _REGION3_SIZE;
                }
        } else {
                asce_limit = _REGION2_SIZE;
                rte_size = _REGION3_SIZE;
        }

        /*
         * Forcing modules and vmalloc area under the ultravisor
         * secure storage limit, so that any vmalloc allocation
         * we do could be used to back secure guest storage.
         *
         * Assume the secure storage limit always exceeds _REGION2_SIZE,
         * otherwise asce_limit and rte_size would have been adjusted.
         */
        vmax = adjust_to_uv_max(asce_limit);
        boot_debug("%d level paging       0x%016lx vmax\n", vmax == _REGION1_SIZE ? 4 : 3, vmax);
#ifdef CONFIG_KASAN
        BUILD_BUG_ON(__NO_KASLR_END_KERNEL > KASAN_SHADOW_START);
        boot_debug("KASAN shadow area:   0x%016lx-0x%016lx\n", KASAN_SHADOW_START, KASAN_SHADOW_END);
        /* force vmalloc and modules below kasan shadow */
        vmax = min(vmax, KASAN_SHADOW_START);
#endif
        vsize = min(vsize, vmax);
        if (kaslr_enabled()) {
                unsigned long kernel_end, kaslr_len, slots, pos;

                kaslr_len = max(KASLR_LEN, vmax - vsize);
                slots = DIV_ROUND_UP(kaslr_len - kernel_size, THREAD_SIZE);
                if (get_random(slots, &pos))
                        pos = 0;
                kernel_end = vmax - pos * THREAD_SIZE;
                kernel_start = round_down(kernel_end - kernel_size, THREAD_SIZE);
                boot_debug("Randomization range: 0x%016lx-0x%016lx\n", vmax - kaslr_len, vmax);
                boot_debug("kernel image:        0x%016lx-0x%016lx (kaslr)\n", kernel_start,
                           kernel_size + kernel_size);
        } else if (vmax < __NO_KASLR_END_KERNEL || vsize > __NO_KASLR_END_KERNEL) {
                kernel_start = round_down(vmax - kernel_size, THREAD_SIZE);
                boot_debug("kernel image:        0x%016lx-0x%016lx (constrained)\n", kernel_start,
                           kernel_start + kernel_size);
        } else {
                kernel_start = __NO_KASLR_START_KERNEL;
                boot_debug("kernel image:        0x%016lx-0x%016lx (nokaslr)\n", kernel_start,
                           kernel_start + kernel_size);
        }
        __kaslr_offset = kernel_start;
        boot_debug("__kaslr_offset:      0x%016lx\n", __kaslr_offset);

        MODULES_END = round_down(kernel_start, _SEGMENT_SIZE);
        MODULES_VADDR = MODULES_END - MODULES_LEN;
        VMALLOC_END = MODULES_VADDR;
        if (IS_ENABLED(CONFIG_KMSAN))
                VMALLOC_END -= MODULES_LEN * 2;
        boot_debug("modules area:        0x%016lx-0x%016lx\n", MODULES_VADDR, MODULES_END);

        /* allow vmalloc area to occupy up to about 1/2 of the rest virtual space left */
        vsize = (VMALLOC_END - FIXMAP_SIZE) / 2;
        vsize = round_down(vsize, _SEGMENT_SIZE);
        vmalloc_size = min(vmalloc_size, vsize);
        if (IS_ENABLED(CONFIG_KMSAN)) {
                /* take 2/3 of vmalloc area for KMSAN shadow and origins */
                vmalloc_size = round_down(vmalloc_size / 3, _SEGMENT_SIZE);
                VMALLOC_END -= vmalloc_size * 2;
        }
        VMALLOC_START = VMALLOC_END - vmalloc_size;
        boot_debug("vmalloc area:        0x%016lx-0x%016lx\n", VMALLOC_START, VMALLOC_END);

        __memcpy_real_area = round_down(VMALLOC_START - MEMCPY_REAL_SIZE, PAGE_SIZE);
        boot_debug("memcpy real area:    0x%016lx-0x%016lx\n", __memcpy_real_area,
                   __memcpy_real_area + MEMCPY_REAL_SIZE);
        __abs_lowcore = round_down(__memcpy_real_area - ABS_LOWCORE_MAP_SIZE,
                                   sizeof(struct lowcore));
        boot_debug("abs lowcore:         0x%016lx-0x%016lx\n", __abs_lowcore,
                   __abs_lowcore + ABS_LOWCORE_MAP_SIZE);

        /* split remaining virtual space between 1:1 mapping & vmemmap array */
        pages = __abs_lowcore / (PAGE_SIZE + sizeof(struct page));
        pages = SECTION_ALIGN_UP(pages);
        /* keep vmemmap_start aligned to a top level region table entry */
        vmemmap_start = round_down(__abs_lowcore - pages * sizeof(struct page), rte_size);
        /* make sure identity map doesn't overlay with vmemmap */
        ident_map_size = min(ident_map_size, vmemmap_start);
        vmemmap_size = SECTION_ALIGN_UP(ident_map_size / PAGE_SIZE) * sizeof(struct page);
        /* make sure vmemmap doesn't overlay with absolute lowcore area */
        if (vmemmap_start + vmemmap_size > __abs_lowcore) {
                vmemmap_size = SECTION_ALIGN_DOWN(ident_map_size / PAGE_SIZE) * sizeof(struct page);
                ident_map_size = vmemmap_size / sizeof(struct page) * PAGE_SIZE;
        }
        vmemmap = (struct page *)vmemmap_start;
        /* maximum address for which linear mapping could be created (DCSS, memory) */
        BUILD_BUG_ON(MAX_DCSS_ADDR > (1UL << MAX_PHYSMEM_BITS));
        max_mappable = max(ident_map_size, MAX_DCSS_ADDR);
        max_mappable = min(max_mappable, vmemmap_start);
#ifdef CONFIG_RANDOMIZE_IDENTITY_BASE
        __identity_base = round_down(vmemmap_start - max_mappable, rte_size);
#endif
        boot_debug("identity map:        0x%016lx-0x%016lx\n", __identity_base,
                   __identity_base + ident_map_size);

        return asce_limit;
}

/*
 * This function clears the BSS section of the decompressed Linux kernel and NOT the decompressor's.
 */
static void clear_bss_section(unsigned long kernel_start)
{
        memset((void *)kernel_start + vmlinux.image_size, 0, vmlinux.bss_size);
}

/*
 * Set vmalloc area size to an 8th of (potential) physical memory
 * size, unless size has been set by kernel command line parameter.
 */
static void setup_vmalloc_size(void)
{
        unsigned long size;

        if (vmalloc_size_set)
                return;
        size = round_up(ident_map_size / 8, _SEGMENT_SIZE);
        vmalloc_size = max(size, vmalloc_size);
}

static void kaslr_adjust_vmlinux_info(long offset)
{
        vmlinux.bootdata_off += offset;
        vmlinux.bootdata_preserved_off += offset;
        vmlinux.got_start += offset;
        vmlinux.got_end += offset;
        vmlinux.init_mm_off += offset;
        vmlinux.swapper_pg_dir_off += offset;
        vmlinux.invalid_pg_dir_off += offset;
        vmlinux.alt_instructions += offset;
        vmlinux.alt_instructions_end += offset;
#ifdef CONFIG_KASAN
        vmlinux.kasan_early_shadow_page_off += offset;
        vmlinux.kasan_early_shadow_pte_off += offset;
        vmlinux.kasan_early_shadow_pmd_off += offset;
        vmlinux.kasan_early_shadow_pud_off += offset;
        vmlinux.kasan_early_shadow_p4d_off += offset;
#endif
}

void startup_kernel(void)
{
        unsigned long vmlinux_size = vmlinux.image_size + vmlinux.bss_size;
        unsigned long nokaslr_text_lma, text_lma = 0, amode31_lma = 0;
        unsigned long kernel_size = TEXT_OFFSET + vmlinux_size;
        unsigned long kaslr_large_page_offset;
        unsigned long max_physmem_end;
        unsigned long asce_limit;
        unsigned long safe_addr;
        psw_t psw;

        setup_lpp();
        store_ipl_parmblock();
        uv_query_info();
        setup_boot_command_line();
        parse_boot_command_line();

        /*
         * Non-randomized kernel physical start address must be _SEGMENT_SIZE
         * aligned (see blow).
         */
        nokaslr_text_lma = ALIGN(mem_safe_offset(), _SEGMENT_SIZE);
        safe_addr = PAGE_ALIGN(nokaslr_text_lma + vmlinux_size);

        /*
         * Reserve decompressor memory together with decompression heap,
         * buffer and memory which might be occupied by uncompressed kernel
         * (if KASLR is off or failed).
         */
        physmem_reserve(RR_DECOMPRESSOR, 0, safe_addr);
        if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && parmarea.initrd_size)
                physmem_reserve(RR_INITRD, parmarea.initrd_start, parmarea.initrd_size);
        oldmem_data.start = parmarea.oldmem_base;
        oldmem_data.size = parmarea.oldmem_size;

        read_ipl_report();
        sclp_early_read_info();
        detect_facilities();
        cmma_init();
        sanitize_prot_virt_host();
        max_physmem_end = detect_max_physmem_end();
        setup_ident_map_size(max_physmem_end);
        setup_vmalloc_size();
        asce_limit = setup_kernel_memory_layout(kernel_size);
        /* got final ident_map_size, physmem allocations could be performed now */
        physmem_set_usable_limit(ident_map_size);
        detect_physmem_online_ranges(max_physmem_end);
        save_ipl_cert_comp_list();
        rescue_initrd(safe_addr, ident_map_size);

        /*
         * __kaslr_offset_phys must be _SEGMENT_SIZE aligned, so the lower
         * 20 bits (the offset within a large page) are zero. Copy the last
         * 20 bits of __kaslr_offset, which is THREAD_SIZE aligned, to
         * __kaslr_offset_phys.
         *
         * With this the last 20 bits of __kaslr_offset_phys and __kaslr_offset
         * are identical, which is required to allow for large mappings of the
         * kernel image.
         */
        kaslr_large_page_offset = __kaslr_offset & ~_SEGMENT_MASK;
        if (kaslr_enabled()) {
                unsigned long size = vmlinux_size + kaslr_large_page_offset;

                text_lma = randomize_within_range(size, _SEGMENT_SIZE, TEXT_OFFSET, ident_map_size);
        }
        if (!text_lma)
                text_lma = nokaslr_text_lma;
        text_lma |= kaslr_large_page_offset;

        /*
         * [__kaslr_offset_phys..__kaslr_offset_phys + TEXT_OFFSET] region is
         * never accessed via the kernel image mapping as per the linker script:
         *
         *      . = TEXT_OFFSET;
         *
         * Therefore, this region could be used for something else and does
         * not need to be reserved. See how it is skipped in setup_vmem().
         */
        __kaslr_offset_phys = text_lma - TEXT_OFFSET;
        kaslr_adjust_vmlinux_info(__kaslr_offset_phys);
        physmem_reserve(RR_VMLINUX, text_lma, vmlinux_size);
        deploy_kernel((void *)text_lma);

        /* vmlinux decompression is done, shrink reserved low memory */
        physmem_reserve(RR_DECOMPRESSOR, 0, (unsigned long)_decompressor_end);

        /*
         * In case KASLR is enabled the randomized location of .amode31
         * section might overlap with .vmlinux.relocs section. To avoid that
         * the below randomize_within_range() could have been called with
         * __vmlinux_relocs_64_end as the lower range address. However,
         * .amode31 section is written to by the decompressed kernel - at
         * that time the contents of .vmlinux.relocs is not needed anymore.
         * Conversely, .vmlinux.relocs is read only by the decompressor, even
         * before the kernel started. Therefore, in case the two sections
         * overlap there is no risk of corrupting any data.
         */
        if (kaslr_enabled()) {
                unsigned long amode31_min;

                amode31_min = (unsigned long)_decompressor_end;
                amode31_lma = randomize_within_range(vmlinux.amode31_size, PAGE_SIZE, amode31_min, SZ_2G);
        }
        if (!amode31_lma)
                amode31_lma = text_lma - vmlinux.amode31_size;
        physmem_reserve(RR_AMODE31, amode31_lma, vmlinux.amode31_size);

        /*
         * The order of the following operations is important:
         *
         * - kaslr_adjust_relocs() must follow clear_bss_section() to establish
         *   static memory references to data in .bss to be used by setup_vmem()
         *   (i.e init_mm.pgd)
         *
         * - setup_vmem() must follow kaslr_adjust_relocs() to be able using
         *   static memory references to data in .bss (i.e init_mm.pgd)
         *
         * - copy_bootdata() must follow setup_vmem() to propagate changes
         *   to bootdata made by setup_vmem()
         */
        clear_bss_section(text_lma);
        kaslr_adjust_relocs(text_lma, text_lma + vmlinux.image_size,
                            __kaslr_offset, __kaslr_offset_phys);
        kaslr_adjust_got(__kaslr_offset);
        setup_vmem(__kaslr_offset, __kaslr_offset + kernel_size, asce_limit);
        dump_physmem_reserved();
        copy_bootdata();
        __apply_alternatives((struct alt_instr *)_vmlinux_info.alt_instructions,
                             (struct alt_instr *)_vmlinux_info.alt_instructions_end,
                             ALT_CTX_EARLY);

        /*
         * Save KASLR offset for early dumps, before vmcore_info is set.
         * Mark as uneven to distinguish from real vmcore_info pointer.
         */
        get_lowcore()->vmcore_info = __kaslr_offset_phys ? __kaslr_offset_phys | 0x1UL : 0;

        /*
         * Jump to the decompressed kernel entry point and switch DAT mode on.
         */
        psw.addr = __kaslr_offset + vmlinux.entry;
        psw.mask = PSW_KERNEL_BITS;
        boot_debug("Starting kernel at:  0x%016lx\n", psw.addr);
        __load_psw(psw);
}