#include <linux/efi.h>
#include <asm/e820/types.h>
#include <asm/processor.h>
#include <asm/efi.h>
#include "pgtable.h"
#include "../string.h"

#define BIOS_START_MIN          0x20000U        /* 128K, less than this is insane */
#define BIOS_START_MAX          0x9f000U        /* 640K, absolute maximum */

#ifdef CONFIG_X86_5LEVEL
/* __pgtable_l5_enabled needs to be in .data to avoid being cleared along with .bss */
unsigned int __section(".data") __pgtable_l5_enabled;
unsigned int __section(".data") pgdir_shift = 39;
unsigned int __section(".data") ptrs_per_p4d = 1;
#endif

struct paging_config {
        unsigned long trampoline_start;
        unsigned long l5_required;
};

/* Buffer to preserve trampoline memory */
static char trampoline_save[TRAMPOLINE_32BIT_SIZE];

/*
 * Trampoline address will be printed by extract_kernel() for debugging
 * purposes.
 *
 * Avoid putting the pointer into .bss as it will be cleared between
 * paging_prepare() and extract_kernel().
 */
unsigned long *trampoline_32bit __section(".data");

extern struct boot_params *boot_params;
int cmdline_find_option_bool(const char *option);

static unsigned long find_trampoline_placement(void)
{
        unsigned long bios_start = 0, ebda_start = 0;
        struct boot_e820_entry *entry;
        char *signature;
        int i;

        /*
         * Find a suitable spot for the trampoline.
         * This code is based on reserve_bios_regions().
         */

        /*
         * EFI systems may not provide legacy ROM. The memory may not be mapped
         * at all.
         *
         * Only look for values in the legacy ROM for non-EFI system.
         */
        signature = (char *)&boot_params->efi_info.efi_loader_signature;
        if (strncmp(signature, EFI32_LOADER_SIGNATURE, 4) &&
            strncmp(signature, EFI64_LOADER_SIGNATURE, 4)) {
                ebda_start = *(unsigned short *)0x40e << 4;
                bios_start = *(unsigned short *)0x413 << 10;
        }

        if (bios_start < BIOS_START_MIN || bios_start > BIOS_START_MAX)
                bios_start = BIOS_START_MAX;

        if (ebda_start > BIOS_START_MIN && ebda_start < bios_start)
                bios_start = ebda_start;

        bios_start = round_down(bios_start, PAGE_SIZE);

        /* Find the first usable memory region under bios_start. */
        for (i = boot_params->e820_entries - 1; i >= 0; i--) {
                unsigned long new = bios_start;

                entry = &boot_params->e820_table[i];

                /* Skip all entries above bios_start. */
                if (bios_start <= entry->addr)
                        continue;

                /* Skip non-RAM entries. */
                if (entry->type != E820_TYPE_RAM)
                        continue;

                /* Adjust bios_start to the end of the entry if needed. */
                if (bios_start > entry->addr + entry->size)
                        new = entry->addr + entry->size;

                /* Keep bios_start page-aligned. */
                new = round_down(new, PAGE_SIZE);

                /* Skip the entry if it's too small. */
                if (new - TRAMPOLINE_32BIT_SIZE < entry->addr)
                        continue;

                /* Protect against underflow. */
                if (new - TRAMPOLINE_32BIT_SIZE > bios_start)
                        break;

                bios_start = new;
                break;
        }

        /* Place the trampoline just below the end of low memory */
        return bios_start - TRAMPOLINE_32BIT_SIZE;
}

struct paging_config paging_prepare(void *rmode)
{
        struct paging_config paging_config = {};

        /* Initialize boot_params. Required for cmdline_find_option_bool(). */
        boot_params = rmode;

        /*
         * Check if LA57 is desired and supported.
         *
         * There are several parts to the check:
         *   - if the kernel supports 5-level paging: CONFIG_X86_5LEVEL=y
         *   - if user asked to disable 5-level paging: no5lvl in cmdline
         *   - if the machine supports 5-level paging:
         *     + CPUID leaf 7 is supported
         *     + the leaf has the feature bit set
         *
         * That's substitute for boot_cpu_has() in early boot code.
         */
        if (IS_ENABLED(CONFIG_X86_5LEVEL) &&
                        !cmdline_find_option_bool("no5lvl") &&
                        native_cpuid_eax(0) >= 7 &&
                        (native_cpuid_ecx(7) & (1 << (X86_FEATURE_LA57 & 31)))) {
                paging_config.l5_required = 1;
        }

        paging_config.trampoline_start = find_trampoline_placement();

        trampoline_32bit = (unsigned long *)paging_config.trampoline_start;

        /* Preserve trampoline memory */
        memcpy(trampoline_save, trampoline_32bit, TRAMPOLINE_32BIT_SIZE);

        /* Clear trampoline memory first */
        memset(trampoline_32bit, 0, TRAMPOLINE_32BIT_SIZE);

        /* Copy trampoline code in place */
        memcpy(trampoline_32bit + TRAMPOLINE_32BIT_CODE_OFFSET / sizeof(unsigned long),
                        &trampoline_32bit_src, TRAMPOLINE_32BIT_CODE_SIZE);

        /*
         * The code below prepares page table in trampoline memory.
         *
         * The new page table will be used by trampoline code for switching
         * from 4- to 5-level paging or vice versa.
         *
         * If switching is not required, the page table is unused: trampoline
         * code wouldn't touch CR3.
         */

        /*
         * We are not going to use the page table in trampoline memory if we
         * are already in the desired paging mode.
         */
        if (paging_config.l5_required == !!(native_read_cr4() & X86_CR4_LA57))
                goto out;

        if (paging_config.l5_required) {
                /*
                 * For 4- to 5-level paging transition, set up current CR3 as
                 * the first and the only entry in a new top-level page table.
                 */
                trampoline_32bit[TRAMPOLINE_32BIT_PGTABLE_OFFSET] = __native_read_cr3() | _PAGE_TABLE_NOENC;
        } else {
                unsigned long src;

                /*
                 * For 5- to 4-level paging transition, copy page table pointed
                 * by first entry in the current top-level page table as our
                 * new top-level page table.
                 *
                 * We cannot just point to the page table from trampoline as it
                 * may be above 4G.
                 */
                src = *(unsigned long *)__native_read_cr3() & PAGE_MASK;
                memcpy(trampoline_32bit + TRAMPOLINE_32BIT_PGTABLE_OFFSET / sizeof(unsigned long),
                       (void *)src, PAGE_SIZE);
        }

out:
        return paging_config;
}

void cleanup_trampoline(void *pgtable)
{
        void *trampoline_pgtable;

        trampoline_pgtable = trampoline_32bit + TRAMPOLINE_32BIT_PGTABLE_OFFSET / sizeof(unsigned long);

        /*
         * Move the top level page table out of trampoline memory,
         * if it's there.
         */
        if ((void *)__native_read_cr3() == trampoline_pgtable) {
                memcpy(pgtable, trampoline_pgtable, PAGE_SIZE);
                native_write_cr3((unsigned long)pgtable);
        }

        /* Restore trampoline memory */
        memcpy(trampoline_32bit, trampoline_save, TRAMPOLINE_32BIT_SIZE);

        /* Initialize variables for 5-level paging */
#ifdef CONFIG_X86_5LEVEL
        if (__read_cr4() & X86_CR4_LA57) {
                __pgtable_l5_enabled = 1;
                pgdir_shift = 48;
                ptrs_per_p4d = 512;
        }
#endif
}