/*
 * Adapted from arm64 version.
 *
 * Copyright (C) 2012 ARM Limited
 * Copyright (C) 2015 Mentor Graphics Corporation.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <linux/elf.h>
#include <linux/err.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/of.h>
#include <linux/printk.h>
#include <linux/slab.h>
#include <linux/timekeeper_internal.h>
#include <linux/vmalloc.h>
#include <asm/arch_timer.h>
#include <asm/barrier.h>
#include <asm/cacheflush.h>
#include <asm/page.h>
#include <asm/vdso.h>
#include <asm/vdso_datapage.h>
#include <clocksource/arm_arch_timer.h>

#define MAX_SYMNAME     64

static struct page **vdso_text_pagelist;

/* Total number of pages needed for the data and text portions of the VDSO. */
unsigned int vdso_total_pages __read_mostly;

/*
 * The VDSO data page.
 */
static union vdso_data_store vdso_data_store __page_aligned_data;
static struct vdso_data *vdso_data = &vdso_data_store.data;

static struct page *vdso_data_page;
static struct vm_special_mapping vdso_data_mapping = {
        .name = "[vvar]",
        .pages = &vdso_data_page,
};

static struct vm_special_mapping vdso_text_mapping = {
        .name = "[vdso]",
};

struct elfinfo {
        Elf32_Ehdr      *hdr;           /* ptr to ELF */
        Elf32_Sym       *dynsym;        /* ptr to .dynsym section */
        unsigned long   dynsymsize;     /* size of .dynsym section */
        char            *dynstr;        /* ptr to .dynstr section */
};

/* Cached result of boot-time check for whether the arch timer exists,
 * and if so, whether the virtual counter is useable.
 */
static bool cntvct_ok __read_mostly;

static bool __init cntvct_functional(void)
{
        struct device_node *np;
        bool ret = false;

        if (!IS_ENABLED(CONFIG_ARM_ARCH_TIMER))
                goto out;

        /* The arm_arch_timer core should export
         * arch_timer_use_virtual or similar so we don't have to do
         * this.
         */
        np = of_find_compatible_node(NULL, NULL, "arm,armv7-timer");
        if (!np)
                goto out_put;

        if (of_property_read_bool(np, "arm,cpu-registers-not-fw-configured"))
                goto out_put;

        ret = true;

out_put:
        of_node_put(np);
out:
        return ret;
}

static void * __init find_section(Elf32_Ehdr *ehdr, const char *name,
                                  unsigned long *size)
{
        Elf32_Shdr *sechdrs;
        unsigned int i;
        char *secnames;

        /* Grab section headers and strings so we can tell who is who */
        sechdrs = (void *)ehdr + ehdr->e_shoff;
        secnames = (void *)ehdr + sechdrs[ehdr->e_shstrndx].sh_offset;

        /* Find the section they want */
        for (i = 1; i < ehdr->e_shnum; i++) {
                if (strcmp(secnames + sechdrs[i].sh_name, name) == 0) {
                        if (size)
                                *size = sechdrs[i].sh_size;
                        return (void *)ehdr + sechdrs[i].sh_offset;
                }
        }

        if (size)
                *size = 0;
        return NULL;
}

static Elf32_Sym * __init find_symbol(struct elfinfo *lib, const char *symname)
{
        unsigned int i;

        for (i = 0; i < (lib->dynsymsize / sizeof(Elf32_Sym)); i++) {
                char name[MAX_SYMNAME], *c;

                if (lib->dynsym[i].st_name == 0)
                        continue;
                strlcpy(name, lib->dynstr + lib->dynsym[i].st_name,
                        MAX_SYMNAME);
                c = strchr(name, '@');
                if (c)
                        *c = 0;
                if (strcmp(symname, name) == 0)
                        return &lib->dynsym[i];
        }
        return NULL;
}

static void __init vdso_nullpatch_one(struct elfinfo *lib, const char *symname)
{
        Elf32_Sym *sym;

        sym = find_symbol(lib, symname);
        if (!sym)
                return;

        sym->st_name = 0;
}

static void __init patch_vdso(void *ehdr)
{
        struct elfinfo einfo;

        einfo = (struct elfinfo) {
                .hdr = ehdr,
        };

        einfo.dynsym = find_section(einfo.hdr, ".dynsym", &einfo.dynsymsize);
        einfo.dynstr = find_section(einfo.hdr, ".dynstr", NULL);

        /* If the virtual counter is absent or non-functional we don't
         * want programs to incur the slight additional overhead of
         * dispatching through the VDSO only to fall back to syscalls.
         */
        if (!cntvct_ok) {
                vdso_nullpatch_one(&einfo, "__vdso_gettimeofday");
                vdso_nullpatch_one(&einfo, "__vdso_clock_gettime");
        }
}

static int __init vdso_init(void)
{
        unsigned int text_pages;
        int i;

        if (memcmp(&vdso_start, "\177ELF", 4)) {
                pr_err("VDSO is not a valid ELF object!\n");
                return -ENOEXEC;
        }

        text_pages = (&vdso_end - &vdso_start) >> PAGE_SHIFT;
        pr_debug("vdso: %i text pages at base %p\n", text_pages, &vdso_start);

        /* Allocate the VDSO text pagelist */
        vdso_text_pagelist = kcalloc(text_pages, sizeof(struct page *),
                                     GFP_KERNEL);
        if (vdso_text_pagelist == NULL)
                return -ENOMEM;

        /* Grab the VDSO data page. */
        vdso_data_page = virt_to_page(vdso_data);

        /* Grab the VDSO text pages. */
        for (i = 0; i < text_pages; i++) {
                struct page *page;

                page = virt_to_page(&vdso_start + i * PAGE_SIZE);
                vdso_text_pagelist[i] = page;
        }

        vdso_text_mapping.pages = vdso_text_pagelist;

        vdso_total_pages = 1; /* for the data/vvar page */
        vdso_total_pages += text_pages;

        cntvct_ok = cntvct_functional();

        patch_vdso(&vdso_start);

        return 0;
}
arch_initcall(vdso_init);

static int install_vvar(struct mm_struct *mm, unsigned long addr)
{
        struct vm_area_struct *vma;

        vma = _install_special_mapping(mm, addr, PAGE_SIZE,
                                       VM_READ | VM_MAYREAD,
                                       &vdso_data_mapping);

        return IS_ERR(vma) ? PTR_ERR(vma) : 0;
}

/* assumes mmap_sem is write-locked */
void arm_install_vdso(struct mm_struct *mm, unsigned long addr)
{
        struct vm_area_struct *vma;
        unsigned long len;

        mm->context.vdso = 0;

        if (vdso_text_pagelist == NULL)
                return;

        if (install_vvar(mm, addr))
                return;

        /* Account for vvar page. */
        addr += PAGE_SIZE;
        len = (vdso_total_pages - 1) << PAGE_SHIFT;

        vma = _install_special_mapping(mm, addr, len,
                VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC,
                &vdso_text_mapping);

        if (!IS_ERR(vma))
                mm->context.vdso = addr;
}

static void vdso_write_begin(struct vdso_data *vdata)
{
        ++vdso_data->seq_count;
        smp_wmb(); /* Pairs with smp_rmb in vdso_read_retry */
}

static void vdso_write_end(struct vdso_data *vdata)
{
        smp_wmb(); /* Pairs with smp_rmb in vdso_read_begin */
        ++vdso_data->seq_count;
}

static bool tk_is_cntvct(const struct timekeeper *tk)
{
        if (!IS_ENABLED(CONFIG_ARM_ARCH_TIMER))
                return false;

        if (strcmp(tk->tkr_mono.clock->name, "arch_sys_counter") != 0)
                return false;

        return true;
}

/**
 * update_vsyscall - update the vdso data page
 *
 * Increment the sequence counter, making it odd, indicating to
 * userspace that an update is in progress.  Update the fields used
 * for coarse clocks and, if the architected system timer is in use,
 * the fields used for high precision clocks.  Increment the sequence
 * counter again, making it even, indicating to userspace that the
 * update is finished.
 *
 * Userspace is expected to sample seq_count before reading any other
 * fields from the data page.  If seq_count is odd, userspace is
 * expected to wait until it becomes even.  After copying data from
 * the page, userspace must sample seq_count again; if it has changed
 * from its previous value, userspace must retry the whole sequence.
 *
 * Calls to update_vsyscall are serialized by the timekeeping core.
 */
void update_vsyscall(struct timekeeper *tk)
{
        struct timespec64 *wtm = &tk->wall_to_monotonic;

        if (!cntvct_ok) {
                /* The entry points have been zeroed, so there is no
                 * point in updating the data page.
                 */
                return;
        }

        vdso_write_begin(vdso_data);

        vdso_data->tk_is_cntvct                 = tk_is_cntvct(tk);
        vdso_data->xtime_coarse_sec             = tk->xtime_sec;
        vdso_data->xtime_coarse_nsec            = (u32)(tk->tkr_mono.xtime_nsec >>
                                                        tk->tkr_mono.shift);
        vdso_data->wtm_clock_sec                = wtm->tv_sec;
        vdso_data->wtm_clock_nsec               = wtm->tv_nsec;

        if (vdso_data->tk_is_cntvct) {
                vdso_data->cs_cycle_last        = tk->tkr_mono.cycle_last;
                vdso_data->xtime_clock_sec      = tk->xtime_sec;
                vdso_data->xtime_clock_snsec    = tk->tkr_mono.xtime_nsec;
                vdso_data->cs_mult              = tk->tkr_mono.mult;
                vdso_data->cs_shift             = tk->tkr_mono.shift;
                vdso_data->cs_mask              = tk->tkr_mono.mask;
        }

        vdso_write_end(vdso_data);

        flush_dcache_page(virt_to_page(vdso_data));
}

void update_vsyscall_tz(void)
{
        vdso_data->tz_minuteswest       = sys_tz.tz_minuteswest;
        vdso_data->tz_dsttime           = sys_tz.tz_dsttime;
        flush_dcache_page(virt_to_page(vdso_data));
}