root/arch/riscv/kernel/hibernate.c 
// SPDX-License-Identifier: GPL-2.0-only
/*
 * Hibernation support for RISCV
 *
 * Copyright (C) 2023 StarFive Technology Co., Ltd.
 *
 * Author: Jee Heng Sia <jeeheng.sia@starfivetech.com>
 */

#include <asm/barrier.h>
#include <asm/cacheflush.h>
#include <asm/mmu_context.h>
#include <asm/page.h>
#include <asm/pgalloc.h>
#include <asm/pgtable.h>
#include <asm/sections.h>
#include <asm/set_memory.h>
#include <asm/smp.h>
#include <asm/suspend.h>

#include <linux/cpu.h>
#include <linux/memblock.h>
#include <linux/pm.h>
#include <linux/sched.h>
#include <linux/suspend.h>
#include <linux/utsname.h>

/* The logical cpu number we should resume on, initialised to a non-cpu number. */
static int sleep_cpu = -EINVAL;

/* Pointer to the temporary resume page table. */
static pgd_t *resume_pg_dir;

/* CPU context to be saved. */
struct suspend_context *hibernate_cpu_context;
EXPORT_SYMBOL_GPL(hibernate_cpu_context);

unsigned long relocated_restore_code;
EXPORT_SYMBOL_GPL(relocated_restore_code);

/**
 * struct arch_hibernate_hdr_invariants - container to store kernel build version.
 * @uts_version: to save the build number and date so that we do not resume with
 *              a different kernel.
 */
struct arch_hibernate_hdr_invariants {
        char            uts_version[__NEW_UTS_LEN + 1];
};

/**
 * struct arch_hibernate_hdr - helper parameters that help us to restore the image.
 * @invariants: container to store kernel build version.
 * @hartid: to make sure same boot_cpu executes the hibernate/restore code.
 * @saved_satp: original page table used by the hibernated image.
 * @restore_cpu_addr: the kernel's image address to restore the CPU context.
 */
static struct arch_hibernate_hdr {
        struct arch_hibernate_hdr_invariants invariants;
        unsigned long   hartid;
        unsigned long   saved_satp;
        unsigned long   restore_cpu_addr;
} resume_hdr;

static void arch_hdr_invariants(struct arch_hibernate_hdr_invariants *i)
{
        memset(i, 0, sizeof(*i));
        memcpy(i->uts_version, init_utsname()->version, sizeof(i->uts_version));
}

/*
 * Check if the given pfn is in the 'nosave' section.
 */
int pfn_is_nosave(unsigned long pfn)
{
        unsigned long nosave_begin_pfn = sym_to_pfn(&__nosave_begin);
        unsigned long nosave_end_pfn = sym_to_pfn(&__nosave_end - 1);

        return ((pfn >= nosave_begin_pfn) && (pfn <= nosave_end_pfn));
}

void notrace save_processor_state(void)
{
}

void notrace restore_processor_state(void)
{
}

/*
 * Helper parameters need to be saved to the hibernation image header.
 */
int arch_hibernation_header_save(void *addr, unsigned int max_size)
{
        struct arch_hibernate_hdr *hdr = addr;

        if (max_size < sizeof(*hdr))
                return -EOVERFLOW;

        arch_hdr_invariants(&hdr->invariants);

        hdr->hartid = cpuid_to_hartid_map(sleep_cpu);
        hdr->saved_satp = csr_read(CSR_SATP);
        hdr->restore_cpu_addr = (unsigned long)__hibernate_cpu_resume;

        return 0;
}
EXPORT_SYMBOL_GPL(arch_hibernation_header_save);

/*
 * Retrieve the helper parameters from the hibernation image header.
 */
int arch_hibernation_header_restore(void *addr)
{
        struct arch_hibernate_hdr_invariants invariants;
        struct arch_hibernate_hdr *hdr = addr;
        int ret = 0;

        arch_hdr_invariants(&invariants);

        if (memcmp(&hdr->invariants, &invariants, sizeof(invariants))) {
                pr_crit("Hibernate image not generated by this kernel!\n");
                return -EINVAL;
        }

        sleep_cpu = riscv_hartid_to_cpuid(hdr->hartid);
        if (sleep_cpu < 0) {
                pr_crit("Hibernated on a CPU not known to this kernel!\n");
                sleep_cpu = -EINVAL;
                return -EINVAL;
        }

#ifdef CONFIG_SMP
        ret = bringup_hibernate_cpu(sleep_cpu);
        if (ret) {
                sleep_cpu = -EINVAL;
                return ret;
        }
#endif
        resume_hdr = *hdr;

        return ret;
}
EXPORT_SYMBOL_GPL(arch_hibernation_header_restore);

int swsusp_arch_suspend(void)
{
        int ret = 0;

        if (__cpu_suspend_enter(hibernate_cpu_context)) {
                sleep_cpu = smp_processor_id();
                suspend_save_csrs(hibernate_cpu_context);
                ret = swsusp_save();
        } else {
                suspend_restore_csrs(hibernate_cpu_context);
                flush_tlb_all();
                flush_icache_all();

                /*
                 * Tell the hibernation core that we've just restored the memory.
                 */
                in_suspend = 0;
                sleep_cpu = -EINVAL;
        }

        return ret;
}

static int temp_pgtable_map_pte(pmd_t *dst_pmdp, pmd_t *src_pmdp, unsigned long start,
                                unsigned long end, pgprot_t prot)
{
        pte_t *src_ptep;
        pte_t *dst_ptep;

        if (pmd_none(READ_ONCE(*dst_pmdp))) {
                dst_ptep = (pte_t *)get_safe_page(GFP_ATOMIC);
                if (!dst_ptep)
                        return -ENOMEM;

                pmd_populate_kernel(NULL, dst_pmdp, dst_ptep);
        }

        dst_ptep = pte_offset_kernel(dst_pmdp, start);
        src_ptep = pte_offset_kernel(src_pmdp, start);

        do {
                pte_t pte = READ_ONCE(*src_ptep);

                if (pte_present(pte))
                        set_pte(dst_ptep, __pte(pte_val(pte) | pgprot_val(prot)));
        } while (dst_ptep++, src_ptep++, start += PAGE_SIZE, start < end);

        return 0;
}

static int temp_pgtable_map_pmd(pud_t *dst_pudp, pud_t *src_pudp, unsigned long start,
                                unsigned long end, pgprot_t prot)
{
        unsigned long next;
        unsigned long ret;
        pmd_t *src_pmdp;
        pmd_t *dst_pmdp;

        if (pud_none(READ_ONCE(*dst_pudp))) {
                dst_pmdp = (pmd_t *)get_safe_page(GFP_ATOMIC);
                if (!dst_pmdp)
                        return -ENOMEM;

                pud_populate(NULL, dst_pudp, dst_pmdp);
        }

        dst_pmdp = pmd_offset(dst_pudp, start);
        src_pmdp = pmd_offset(src_pudp, start);

        do {
                pmd_t pmd = READ_ONCE(*src_pmdp);

                next = pmd_addr_end(start, end);

                if (pmd_none(pmd))
                        continue;

                if (pmd_leaf(pmd)) {
                        set_pmd(dst_pmdp, __pmd(pmd_val(pmd) | pgprot_val(prot)));
                } else {
                        ret = temp_pgtable_map_pte(dst_pmdp, src_pmdp, start, next, prot);
                        if (ret)
                                return -ENOMEM;
                }
        } while (dst_pmdp++, src_pmdp++, start = next, start != end);

        return 0;
}

static int temp_pgtable_map_pud(p4d_t *dst_p4dp, p4d_t *src_p4dp, unsigned long start,
                                unsigned long end, pgprot_t prot)
{
        unsigned long next;
        unsigned long ret;
        pud_t *dst_pudp;
        pud_t *src_pudp;

        if (p4d_none(READ_ONCE(*dst_p4dp))) {
                dst_pudp = (pud_t *)get_safe_page(GFP_ATOMIC);
                if (!dst_pudp)
                        return -ENOMEM;

                p4d_populate(NULL, dst_p4dp, dst_pudp);
        }

        dst_pudp = pud_offset(dst_p4dp, start);
        src_pudp = pud_offset(src_p4dp, start);

        do {
                pud_t pud = READ_ONCE(*src_pudp);

                next = pud_addr_end(start, end);

                if (pud_none(pud))
                        continue;

                if (pud_leaf(pud)) {
                        set_pud(dst_pudp, __pud(pud_val(pud) | pgprot_val(prot)));
                } else {
                        ret = temp_pgtable_map_pmd(dst_pudp, src_pudp, start, next, prot);
                        if (ret)
                                return -ENOMEM;
                }
        } while (dst_pudp++, src_pudp++, start = next, start != end);

        return 0;
}

static int temp_pgtable_map_p4d(pgd_t *dst_pgdp, pgd_t *src_pgdp, unsigned long start,
                                unsigned long end, pgprot_t prot)
{
        unsigned long next;
        unsigned long ret;
        p4d_t *dst_p4dp;
        p4d_t *src_p4dp;

        if (pgd_none(READ_ONCE(*dst_pgdp))) {
                dst_p4dp = (p4d_t *)get_safe_page(GFP_ATOMIC);
                if (!dst_p4dp)
                        return -ENOMEM;

                pgd_populate(NULL, dst_pgdp, dst_p4dp);
        }

        dst_p4dp = p4d_offset(dst_pgdp, start);
        src_p4dp = p4d_offset(src_pgdp, start);

        do {
                p4d_t p4d = READ_ONCE(*src_p4dp);

                next = p4d_addr_end(start, end);

                if (p4d_none(p4d))
                        continue;

                if (p4d_leaf(p4d)) {
                        set_p4d(dst_p4dp, __p4d(p4d_val(p4d) | pgprot_val(prot)));
                } else {
                        ret = temp_pgtable_map_pud(dst_p4dp, src_p4dp, start, next, prot);
                        if (ret)
                                return -ENOMEM;
                }
        } while (dst_p4dp++, src_p4dp++, start = next, start != end);

        return 0;
}

static int temp_pgtable_mapping(pgd_t *pgdp, unsigned long start, unsigned long end, pgprot_t prot)
{
        pgd_t *dst_pgdp = pgd_offset_pgd(pgdp, start);
        pgd_t *src_pgdp = pgd_offset_k(start);
        unsigned long next;
        unsigned long ret;

        do {
                pgd_t pgd = READ_ONCE(*src_pgdp);

                next = pgd_addr_end(start, end);

                if (pgd_none(pgd))
                        continue;

                if (pgd_leaf(pgd)) {
                        set_pgd(dst_pgdp, __pgd(pgd_val(pgd) | pgprot_val(prot)));
                } else {
                        ret = temp_pgtable_map_p4d(dst_pgdp, src_pgdp, start, next, prot);
                        if (ret)
                                return -ENOMEM;
                }
        } while (dst_pgdp++, src_pgdp++, start = next, start != end);

        return 0;
}

static unsigned long relocate_restore_code(void)
{
        void *page = (void *)get_safe_page(GFP_ATOMIC);

        if (!page)
                return -ENOMEM;

        copy_page(page, hibernate_core_restore_code);

        /* Make the page containing the relocated code executable. */
        set_memory_x((unsigned long)page, 1);

        return (unsigned long)page;
}

int swsusp_arch_resume(void)
{
        unsigned long end = (unsigned long)pfn_to_virt(max_low_pfn);
        unsigned long start = PAGE_OFFSET;
        int ret;

        /*
         * Memory allocated by get_safe_page() will be dealt with by the hibernation core,
         * we don't need to free it here.
         */
        resume_pg_dir = (pgd_t *)get_safe_page(GFP_ATOMIC);
        if (!resume_pg_dir)
                return -ENOMEM;

        /*
         * Create a temporary page table and map the whole linear region as executable and
         * writable.
         */
        ret = temp_pgtable_mapping(resume_pg_dir, start, end, __pgprot(_PAGE_WRITE | _PAGE_EXEC));
        if (ret)
                return ret;

        /* Move the restore code to a new page so that it doesn't get overwritten by itself. */
        relocated_restore_code = relocate_restore_code();
        if (relocated_restore_code == -ENOMEM)
                return -ENOMEM;

        /*
         * Map the __hibernate_cpu_resume() address to the temporary page table so that the
         * restore code can jumps to it after finished restore the image. The next execution
         * code doesn't find itself in a different address space after switching over to the
         * original page table used by the hibernated image.
         * The __hibernate_cpu_resume() mapping is unnecessary for RV32 since the kernel and
         * linear addresses are identical, but different for RV64. To ensure consistency, we
         * map it for both RV32 and RV64 kernels.
         * Additionally, we should ensure that the page is writable before restoring the image.
         */
        start = (unsigned long)resume_hdr.restore_cpu_addr;
        end = start + PAGE_SIZE;

        ret = temp_pgtable_mapping(resume_pg_dir, start, end, __pgprot(_PAGE_WRITE));
        if (ret)
                return ret;

        hibernate_restore_image(resume_hdr.saved_satp, (PFN_DOWN(__pa(resume_pg_dir)) | satp_mode),
                                resume_hdr.restore_cpu_addr);

        return 0;
}

#ifdef CONFIG_PM_SLEEP_SMP
int hibernate_resume_nonboot_cpu_disable(void)
{
        if (sleep_cpu < 0) {
                pr_err("Failing to resume from hibernate on an unknown CPU\n");
                return -ENODEV;
        }

        return freeze_secondary_cpus(sleep_cpu);
}
#endif

static int __init riscv_hibernate_init(void)
{
        hibernate_cpu_context = kzalloc_obj(*hibernate_cpu_context);

        if (WARN_ON(!hibernate_cpu_context))
                return -ENOMEM;

        return 0;
}

early_initcall(riscv_hibernate_init);