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Commit b2a68c23 authored by Michael Holzheu's avatar Michael Holzheu Committed by Martin Schwidefsky
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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: default avatarMichael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 6022afc0

arch/s390/include/asm/io.h

+2 −5
Original line number Diff line number Diff line
@@ -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

arch/s390/mm/maccess.c

+67 −0
Original line number Diff line number Diff line
@@ -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);

}