s390/mm: rework memcpy_real() to avoid DAT-off mode

Function memcpy_real() is an univeral data mover that does not
require DAT mode to be able reading from a physical address.
Its advantage is an ability to read from any address, even
those for which no kernel virtual mapping exists.

Although memcpy_real() is interrupt-safe, there are no handlers
that make use of this function. The compiler instrumentation
have to be disabled and separate no-DAT stack used to allow
execution of the function once DAT mode is disabled.

Rework memcpy_real() to overcome these shortcomings. As result,
data copying (which is primarily reading out a crashed system
memory by a user process) is executed on a regular stack with
enabled interrupts. Also, use of memcpy_real_buf swap buffer
becomes unnecessary and the swapping is eliminated.

The above is achieved by using a fixed virtual address range
that spans a single page and remaps that page repeatedly when
memcpy_real() is called for a particular physical address.

Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/s390/char/zcore.c b/drivers/s390/char/zcore.c
index f6da215ccf9f..6165e6aae762 100644
--- a/drivers/s390/char/zcore.c
+++ b/drivers/s390/char/zcore.c
@@ -30,6 +30,7 @@
 #include <asm/checksum.h>
 #include <asm/os_info.h>
 #include <asm/switch_to.h>
+#include <asm/maccess.h>
 #include "sclp.h"
 
 #define TRACE(x...) debug_sprintf_event(zcore_dbf, 1, x)