2 files changed, 62 insertions, 1 deletions

diff --git a/arch/s390/mm/Makefile b/arch/s390/mm/Makefile
index 2a7458134544..db05661ac895 100644
--- a/arch/s390/mm/Makefile
+++ b/arch/s390/mm/Makefile
@@ -2,7 +2,7 @@
 # Makefile for the linux s390-specific parts of the memory manager.
 #
 
-obj-y    := init.o fault.o extmem.o mmap.o vmem.o pgtable.o
+obj-y    := init.o fault.o extmem.o mmap.o vmem.o pgtable.o maccess.o
 obj-$(CONFIG_CMM) += cmm.o
 obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
 obj-$(CONFIG_PAGE_STATES) += page-states.o
diff --git a/arch/s390/mm/maccess.c b/arch/s390/mm/maccess.c
new file mode 100644
index 000000000000..81756271dc44
--- /dev/null
+++ b/arch/s390/mm/maccess.c
@@ -0,0 +1,61 @@
+/*
+ * Access kernel memory without faulting -- s390 specific implementation.
+ *
+ * Copyright IBM Corp. 2009
+ *
+ *   Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
+ *
+ */
+
+#include <linux/uaccess.h>
+#include <linux/kernel.h>
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <asm/system.h>
+
+/*
+ * This function writes to kernel memory bypassing DAT and possible
+ * write protection. It copies one to four bytes from src to dst
+ * using the stura instruction.
+ * Returns the number of bytes copied or -EFAULT.
+ */
+static long probe_kernel_write_odd(void *dst, void *src, size_t size)
+{
+        unsigned long count, aligned;
+        int offset, mask;
+        int rc = -EFAULT;
+
+        aligned = (unsigned long) dst & ~3UL;
+        offset = (unsigned long) dst & 3;
+        count = min_t(unsigned long, 4 - offset, size);
+        mask = (0xf << (4 - count)) & 0xf;
+        mask >>= offset;
+        asm volatile(
+                "       bras    1,0f\n"
+                "       icm     0,0,0(%3)\n"
+                "0:     l       0,0(%1)\n"
+                "       lra     %1,0(%1)\n"
+                "1:     ex      %2,0(1)\n"
+                "2:     stura   0,%1\n"
+                "       la      %0,0\n"
+                "3:\n"
+                EX_TABLE(0b,3b) EX_TABLE(1b,3b) EX_TABLE(2b,3b)
+                : "+d" (rc), "+a" (aligned)
+                : "a" (mask), "a" (src) : "cc", "memory", "0", "1");
+        return rc ? rc : count;
+}
+
+long probe_kernel_write(void *dst, void *src, size_t size)
+{
+        long copied = 0;
+
+        while (size) {
+                copied = probe_kernel_write_odd(dst, src, size);
+                if (copied < 0)
+                        break;
+                dst += copied;
+                src += copied;
+                size -= copied;
+        }
+        return copied < 0 ? -EFAULT : 0;
+}