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s390: allow absolute memory access for /dev/mem

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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>
This commit is contained in:
Michael Holzheu 2012-05-09 16:27:36 +02:00 committed by Martin Schwidefsky
parent 6022afc060
commit b2a68c2356
2 changed files with 69 additions and 5 deletions
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7
arch/s390/include/asm/io.h
View File

@ -38,11 +38,8 @@ static inline void * phys_to_virt(unsigned long address)
return (void *) address;
}
/*
* Convert a physical pointer to a virtual kernel pointer for /dev/mem
* access
*/
#define xlate_dev_mem_ptr(p) __va(p)
void *xlate_dev_mem_ptr(unsigned long phys);
void unxlate_dev_mem_ptr(unsigned long phys, void *addr);
/*
* Convert a virtual cached pointer to an uncached pointer

67
arch/s390/mm/maccess.c
View File

@ -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 @@ int copy_from_user_real(void *dest, void __user *src, size_t count)
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);
}