// SPDX-License-Identifier: GPL-2.0
/*
 * Access kernel memory without faulting -- s390 specific implementation.
 *
 * Copyright IBM Corp. 2009, 2015
 *
 */

#include <linux/uaccess.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/gfp.h>
#include <linux/cpu.h>
#include <linux/uio.h>
#include <linux/io.h>
#include <asm/asm-extable.h>
#include <asm/abs_lowcore.h>
#include <asm/stacktrace.h>
#include <asm/sections.h>
#include <asm/maccess.h>
#include <asm/ctlreg.h>

unsigned long __bootdata_preserved(__memcpy_real_area);
pte_t *__bootdata_preserved(memcpy_real_ptep);
static DEFINE_MUTEX(memcpy_real_mutex);

static notrace long s390_kernel_write_odd(void *dst, const void *src, size_t size)
{
        unsigned long aligned, offset, count;
        char tmp[8];

        aligned = (unsigned long) dst & ~7UL;
        offset = (unsigned long) dst & 7UL;
        size = min(8UL - offset, size);
        count = size - 1;
        asm volatile(
                "       bras    1,0f\n"
                "       mvc     0(1,%4),0(%5)\n"
                "0:     mvc     0(8,%3),0(%0)\n"
                "       ex      %1,0(1)\n"
                "       lg      %1,0(%3)\n"
                "       lra     %0,0(%0)\n"
                "       sturg   %1,%0"
                : "+&a" (aligned), "+&a" (count), "=m" (tmp)
                : "a" (&tmp), "a" (&tmp[offset]), "a" (src)
                : "cc", "memory", "1");
        return size;
}

/*
 * __s390_kernel_write - write to kernel memory bypassing DAT
 * @dst: destination address
 * @src: source address
 * @size: number of bytes to copy
 *
 * This function writes to kernel memory bypassing DAT and possible page table
 * write protection. It writes to the destination using the sturg instruction.
 * Therefore we have a read-modify-write sequence: the function reads eight
 * bytes from destination at an eight byte boundary, modifies the bytes
 * requested and writes the result back in a loop.
 */
static DEFINE_SPINLOCK(s390_kernel_write_lock);

notrace void *__s390_kernel_write(void *dst, const void *src, size_t size)
{
        void *tmp = dst;
        unsigned long flags;
        long copied;

        spin_lock_irqsave(&s390_kernel_write_lock, flags);
        while (size) {
                copied = s390_kernel_write_odd(tmp, src, size);
                tmp += copied;
                src += copied;
                size -= copied;
        }
        spin_unlock_irqrestore(&s390_kernel_write_lock, flags);

        return dst;
}

size_t memcpy_real_iter(struct iov_iter *iter, unsigned long src, size_t count)
{
        size_t len, copied, res = 0;
        unsigned long phys, offset;
        void *chunk;
        pte_t pte;

        BUILD_BUG_ON(MEMCPY_REAL_SIZE != PAGE_SIZE);
        while (count) {
                phys = src & MEMCPY_REAL_MASK;
                offset = src & ~MEMCPY_REAL_MASK;
                chunk = (void *)(__memcpy_real_area + offset);
                len = min(count, MEMCPY_REAL_SIZE - offset);
                pte = mk_pte_phys(phys, PAGE_KERNEL_RO);

                mutex_lock(&memcpy_real_mutex);
                if (pte_val(pte) != pte_val(*memcpy_real_ptep)) {
                        __ptep_ipte(__memcpy_real_area, memcpy_real_ptep, 0, 0, IPTE_GLOBAL);
                        set_pte(memcpy_real_ptep, pte);
                }
                copied = copy_to_iter(chunk, len, iter);
                mutex_unlock(&memcpy_real_mutex);

                count -= copied;
                src += copied;
                res += copied;
                if (copied < len)
                        break;
        }
        return res;
}

int memcpy_real(void *dest, unsigned long src, size_t count)
{
        struct iov_iter iter;
        struct kvec kvec;

        kvec.iov_base = dest;
        kvec.iov_len = count;
        iov_iter_kvec(&iter, ITER_DEST, &kvec, 1, count);
        if (memcpy_real_iter(&iter, src, count) < count)
                return -EFAULT;
        return 0;
}

/*
 * Find CPU that owns swapped prefix page
 */
static int get_swapped_owner(phys_addr_t addr)
{
        phys_addr_t lc;
        int cpu;

        for_each_online_cpu(cpu) {
                lc = virt_to_phys(lowcore_ptr[cpu]);
                if (addr > lc + sizeof(struct lowcore) - 1 || addr < lc)
                        continue;
                return cpu;
        }
        return -1;
}

/*
 * Convert a physical pointer for /dev/mem access
 *
 * For swapped prefix pages a new buffer is returned that contains a copy of
 * the absolute memory. The buffer size is maximum one page large.
 */
void *xlate_dev_mem_ptr(phys_addr_t addr)
{
        void *ptr = phys_to_virt(addr);
        void *bounce = ptr;
        struct lowcore *abs_lc;
        unsigned long size;
        int this_cpu, cpu;

        cpus_read_lock();
        this_cpu = get_cpu();
        if (addr >= sizeof(struct lowcore)) {
                cpu = get_swapped_owner(addr);
                if (cpu < 0)
                        goto out;
        }
        bounce = (void *)__get_free_page(GFP_ATOMIC);
        if (!bounce)
                goto out;
        size = PAGE_SIZE - (addr & ~PAGE_MASK);
        if (addr < sizeof(struct lowcore)) {
                abs_lc = get_abs_lowcore();
                ptr = (void *)abs_lc + addr;
                memcpy(bounce, ptr, size);
                put_abs_lowcore(abs_lc);
        } else if (cpu == this_cpu) {
                ptr = (void *)(addr - virt_to_phys(lowcore_ptr[cpu]));
                memcpy(bounce, ptr, size);
        } else {
                memcpy(bounce, ptr, size);
        }
out:
        put_cpu();
        cpus_read_unlock();
        return bounce;
}

/*
 * Free converted buffer for /dev/mem access (if necessary)
 */
void unxlate_dev_mem_ptr(phys_addr_t addr, void *ptr)
{
        if (addr != virt_to_phys(ptr))
                free_page((unsigned long)ptr);
}