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authorMichael Holzheu <holzheu@linux.vnet.ibm.com>2012-05-09 16:27:36 +0200
committerMartin Schwidefsky <schwidefsky@de.ibm.com>2012-05-16 14:42:38 +0200
commitb2a68c235663c65365c4b4424c6e6c5ee90ae3a1 (patch)
tree2602a18a860e0dadd9a1332e6b9dd81f26ffb301 /arch/s390/mm/maccess.c
parent6022afc060425864c33f4ab62bbe41d20ac85362 (diff)
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s390: allow absolute memory access for /dev/mem
Currently dev/mem for s390 provides only real memory access. This means that the CPU prefix pages are swapped. The prefix swap for real memory works as follows: Each CPU owns a prefix register that points to a page aligned memory location "P". If this CPU accesses the address range [0,0x1fff], it is translated by the hardware to [P,P+0x1fff]. Accordingly if this CPU accesses the address range [P,P+0x1fff], it is translated by the hardware to [0,0x1fff]. Therefore, if [P,P+0x1fff] or [0,0x1fff] is read from the current /dev/mem device, the incorrectly swapped memory content is returned. With this patch the /dev/mem architecture code is modified to provide absolute memory access. This is done via the arch specific functions xlate_dev_mem_ptr() and unxlate_dev_mem_ptr(). For swapped pages on s390 the function xlate_dev_mem_ptr() now returns a new buffer with a copy of the requested absolute memory. In case the buffer was allocated, the unxlate_dev_mem_ptr() function frees it after /dev/mem code has called copy_to_user(). Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Diffstat (limited to 'arch/s390/mm/maccess.c')
-rw-r--r--arch/s390/mm/maccess.c67
1 files changed, 67 insertions, 0 deletions
diff --git a/arch/s390/mm/maccess.c b/arch/s390/mm/maccess.c
index e1335dc2b1b7..795a0a9bb2eb 100644
--- a/arch/s390/mm/maccess.c
+++ b/arch/s390/mm/maccess.c
@@ -12,6 +12,7 @@
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/gfp.h>
+#include <linux/cpu.h>
#include <asm/ctl_reg.h>
/*
@@ -166,3 +167,69 @@ out:
free_page((unsigned long) buf);
return rc;
}
+
+/*
+ * Check if physical address is within prefix or zero page
+ */
+static int is_swapped(unsigned long addr)
+{
+ unsigned long lc;
+ int cpu;
+
+ if (addr < sizeof(struct _lowcore))
+ return 1;
+ for_each_online_cpu(cpu) {
+ lc = (unsigned long) lowcore_ptr[cpu];
+ if (addr > lc + sizeof(struct _lowcore) - 1 || addr < lc)
+ continue;
+ return 1;
+ }
+ return 0;
+}
+
+/*
+ * Return swapped prefix or zero page address
+ */
+static unsigned long get_swapped(unsigned long addr)
+{
+ unsigned long prefix = store_prefix();
+
+ if (addr < sizeof(struct _lowcore))
+ return addr + prefix;
+ if (addr >= prefix && addr < prefix + sizeof(struct _lowcore))
+ return addr - prefix;
+ return addr;
+}
+
+/*
+ * 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(unsigned long addr)
+{
+ void *bounce = (void *) addr;
+ unsigned long size;
+
+ get_online_cpus();
+ preempt_disable();
+ if (is_swapped(addr)) {
+ size = PAGE_SIZE - (addr & ~PAGE_MASK);
+ bounce = (void *) __get_free_page(GFP_ATOMIC);
+ if (bounce)
+ memcpy_real(bounce, (void *) get_swapped(addr), size);
+ }
+ preempt_enable();
+ put_online_cpus();
+ return bounce;
+}
+
+/*
+ * Free converted buffer for /dev/mem access (if necessary)
+ */
+void unxlate_dev_mem_ptr(unsigned long addr, void *buf)
+{
+ if ((void *) addr != buf)
+ free_page((unsigned long) buf);
+}