// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright IBM Corp. 2004, 2010
 * Interface implementation for communication with the z/VM control program
 *
 * Author(s): Christian Borntraeger <borntraeger@de.ibm.com>
 *
 * z/VMs CP offers the possibility to issue commands via the diagnose code 8
 * this driver implements a character device that issues these commands and
 * returns the answer of CP.
 *
 * The idea of this driver is based on cpint from Neale Ferguson and #CP in CMS
 */

#include <linux/fs.h>
#include <linux/init.h>
#include <linux/compat.h>
#include <linux/kernel.h>
#include <linux/miscdevice.h>
#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/export.h>
#include <linux/mutex.h>
#include <linux/cma.h>
#include <linux/mm.h>
#include <asm/cpcmd.h>
#include <asm/debug.h>
#include <asm/vmcp.h>

struct vmcp_session {
        char *response;
        unsigned int bufsize;
        unsigned int cma_alloc : 1;
        int resp_size;
        int resp_code;
        struct mutex mutex;
};

static debug_info_t *vmcp_debug;

static unsigned long vmcp_cma_size __initdata = CONFIG_VMCP_CMA_SIZE * 1024 * 1024;
static struct cma *vmcp_cma;

static int __init early_parse_vmcp_cma(char *p)
{
        if (!p)
                return 1;
        vmcp_cma_size = ALIGN(memparse(p, NULL), PAGE_SIZE);
        return 0;
}
early_param("vmcp_cma", early_parse_vmcp_cma);

void __init vmcp_cma_reserve(void)
{
        if (!MACHINE_IS_VM)
                return;
        cma_declare_contiguous(0, vmcp_cma_size, 0, 0, 0, false, "vmcp", &vmcp_cma);
}

static void vmcp_response_alloc(struct vmcp_session *session)
{
        struct page *page = NULL;
        int nr_pages, order;

        order = get_order(session->bufsize);
        nr_pages = ALIGN(session->bufsize, PAGE_SIZE) >> PAGE_SHIFT;
        /*
         * For anything below order 3 allocations rely on the buddy
         * allocator. If such low-order allocations can't be handled
         * anymore the system won't work anyway.
         */
        if (order > 2)
                page = cma_alloc(vmcp_cma, nr_pages, 0, false);
        if (page) {
                session->response = (char *)page_to_phys(page);
                session->cma_alloc = 1;
                return;
        }
        session->response = (char *)__get_free_pages(GFP_KERNEL | __GFP_RETRY_MAYFAIL, order);
}

static void vmcp_response_free(struct vmcp_session *session)
{
        int nr_pages, order;
        struct page *page;

        if (!session->response)
                return;
        order = get_order(session->bufsize);
        nr_pages = ALIGN(session->bufsize, PAGE_SIZE) >> PAGE_SHIFT;
        if (session->cma_alloc) {
                page = phys_to_page((unsigned long)session->response);
                cma_release(vmcp_cma, page, nr_pages);
                session->cma_alloc = 0;
        } else {
                free_pages((unsigned long)session->response, order);
        }
        session->response = NULL;
}

static int vmcp_open(struct inode *inode, struct file *file)
{
        struct vmcp_session *session;

        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;

        session = kmalloc(sizeof(*session), GFP_KERNEL);
        if (!session)
                return -ENOMEM;

        session->bufsize = PAGE_SIZE;
        session->response = NULL;
        session->resp_size = 0;
        mutex_init(&session->mutex);
        file->private_data = session;
        return nonseekable_open(inode, file);
}

static int vmcp_release(struct inode *inode, struct file *file)
{
        struct vmcp_session *session;

        session = file->private_data;
        file->private_data = NULL;
        vmcp_response_free(session);
        kfree(session);
        return 0;
}

static ssize_t
vmcp_read(struct file *file, char __user *buff, size_t count, loff_t *ppos)
{
        ssize_t ret;
        size_t size;
        struct vmcp_session *session;

        session = file->private_data;
        if (mutex_lock_interruptible(&session->mutex))
                return -ERESTARTSYS;
        if (!session->response) {
                mutex_unlock(&session->mutex);
                return 0;
        }
        size = min_t(size_t, session->resp_size, session->bufsize);
        ret = simple_read_from_buffer(buff, count, ppos,
                                        session->response, size);

        mutex_unlock(&session->mutex);

        return ret;
}

static ssize_t
vmcp_write(struct file *file, const char __user *buff, size_t count,
           loff_t *ppos)
{
        char *cmd;
        struct vmcp_session *session;

        if (count > 240)
                return -EINVAL;
        cmd = memdup_user_nul(buff, count);
        if (IS_ERR(cmd))
                return PTR_ERR(cmd);
        session = file->private_data;
        if (mutex_lock_interruptible(&session->mutex)) {
                kfree(cmd);
                return -ERESTARTSYS;
        }
        if (!session->response)
                vmcp_response_alloc(session);
        if (!session->response) {
                mutex_unlock(&session->mutex);
                kfree(cmd);
                return -ENOMEM;
        }
        debug_text_event(vmcp_debug, 1, cmd);
        session->resp_size = cpcmd(cmd, session->response, session->bufsize,
                                   &session->resp_code);
        mutex_unlock(&session->mutex);
        kfree(cmd);
        *ppos = 0;              /* reset the file pointer after a command */
        return count;
}


/*
 * These ioctls are available, as the semantics of the diagnose 8 call
 * does not fit very well into a Linux call. Diagnose X'08' is described in
 * CP Programming Services SC24-6084-00
 *
 * VMCP_GETCODE: gives the CP return code back to user space
 * VMCP_SETBUF: sets the response buffer for the next write call. diagnose 8
 * expects adjacent pages in real storage and to make matters worse, we
 * dont know the size of the response. Therefore we default to PAGESIZE and
 * let userspace to change the response size, if userspace expects a bigger
 * response
 */
static long vmcp_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
        struct vmcp_session *session;
        int ret = -ENOTTY;
        int __user *argp;

        session = file->private_data;
        if (is_compat_task())
                argp = compat_ptr(arg);
        else
                argp = (int __user *)arg;
        if (mutex_lock_interruptible(&session->mutex))
                return -ERESTARTSYS;
        switch (cmd) {
        case VMCP_GETCODE:
                ret = put_user(session->resp_code, argp);
                break;
        case VMCP_SETBUF:
                vmcp_response_free(session);
                ret = get_user(session->bufsize, argp);
                if (ret)
                        session->bufsize = PAGE_SIZE;
                if (!session->bufsize || get_order(session->bufsize) > 8) {
                        session->bufsize = PAGE_SIZE;
                        ret = -EINVAL;
                }
                break;
        case VMCP_GETSIZE:
                ret = put_user(session->resp_size, argp);
                break;
        default:
                break;
        }
        mutex_unlock(&session->mutex);
        return ret;
}

static const struct file_operations vmcp_fops = {
        .owner          = THIS_MODULE,
        .open           = vmcp_open,
        .release        = vmcp_release,
        .read           = vmcp_read,
        .write          = vmcp_write,
        .unlocked_ioctl = vmcp_ioctl,
        .compat_ioctl   = vmcp_ioctl,
        .llseek         = no_llseek,
};

static struct miscdevice vmcp_dev = {
        .name   = "vmcp",
        .minor  = MISC_DYNAMIC_MINOR,
        .fops   = &vmcp_fops,
};

static int __init vmcp_init(void)
{
        int ret;

        if (!MACHINE_IS_VM)
                return 0;

        vmcp_debug = debug_register("vmcp", 1, 1, 240);
        if (!vmcp_debug)
                return -ENOMEM;

        ret = debug_register_view(vmcp_debug, &debug_hex_ascii_view);
        if (ret) {
                debug_unregister(vmcp_debug);
                return ret;
        }

        ret = misc_register(&vmcp_dev);
        if (ret)
                debug_unregister(vmcp_debug);
        return ret;
}
device_initcall(vmcp_init);