Commit 340a9828 authored by Giulio Benetti's avatar Giulio Benetti Committed by Russell King (Oracle)
Browse files

ARM: 9266/1: mm: fix no-MMU ZERO_PAGE() implementation 

Actually in no-MMU SoCs(i.e. i.MXRT) ZERO_PAGE(vaddr) expands to
```
virt_to_page(0)
```
that in order expands to:
```
pfn_to_page(virt_to_pfn(0))
```
and then virt_to_pfn(0) to:
```
        ((((unsigned long)(0) - PAGE_OFFSET) >> PAGE_SHIFT) +
         PHYS_PFN_OFFSET)
```
where PAGE_OFFSET and PHYS_PFN_OFFSET are the DRAM offset(0x80000000) and
PAGE_SHIFT is 12. This way we obtain 16MB(0x01000000) summed to the base of
DRAM(0x80000000).
When ZERO_PAGE(0) is then used, for example in bio_add_page(), the page
gets an address that is out of DRAM bounds.
So instead of using fake virtual page 0 let's allocate a dedicated
zero_page during paging_init() and assign it to a global 'struct page *
empty_zero_page' the same way mmu.c does and it's the same approach used
in m68k with commit dc068f46 as discussed here[0]. Then let's move
ZERO_PAGE() definition to the top of pgtable.h to be in common between
mmu.c and nommu.c.

[0]: https://lore.kernel.org/linux-m68k/2a462b23-5b8e-bbf4-ec7d-778434a3b9d7@google.com/T/#m1266ceb63


ad140743174d6b3070364d3c9a5179b

Signed-off-by: default avatarGiulio Benetti <giulio.benetti@benettiengineering.com>
Reviewed-by: default avatarArnd Bergmann <arnd@arndb.de>
Signed-off-by: default avatarRussell King (Oracle) <rmk+kernel@armlinux.org.uk>
parent 612695bc

arch/arm/include/asm/pgtable-nommu.h

+0 −6
Original line number Diff line number Diff line
@@ -44,12 +44,6 @@ 


typedef pte_t *pte_addr_t;



/*

 * ZERO_PAGE is a global shared page that is always zero: used

 * for zero-mapped memory areas etc..

 */

#define ZERO_PAGE(vaddr)	(virt_to_page(0))



/*

 * Mark the prot value as uncacheable and unbufferable.

 */

arch/arm/include/asm/pgtable.h

+9 −7
Original line number Diff line number Diff line
@@ -10,6 +10,15 @@ 
#include <linux/const.h>

#include <asm/proc-fns.h>



#ifndef __ASSEMBLY__

/*

 * ZERO_PAGE is a global shared page that is always zero: used

 * for zero-mapped memory areas etc..

 */

extern struct page *empty_zero_page;

#define ZERO_PAGE(vaddr)	(empty_zero_page)

#endif



#ifndef CONFIG_MMU



#include <asm-generic/pgtable-nopud.h>
@@ -139,13 +148,6 @@ extern pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn, 
 */



#ifndef __ASSEMBLY__

/*

 * ZERO_PAGE is a global shared page that is always zero: used

 * for zero-mapped memory areas etc..

 */

extern struct page *empty_zero_page;

#define ZERO_PAGE(vaddr)	(empty_zero_page)





extern pgd_t swapper_pg_dir[PTRS_PER_PGD];

arch/arm/mm/nommu.c

+19 −0
Original line number Diff line number Diff line
@@ -26,6 +26,13 @@ 


unsigned long vectors_base;



/*

 * empty_zero_page is a special page that is used for

 * zero-initialized data and COW.

 */

struct page *empty_zero_page;

EXPORT_SYMBOL(empty_zero_page);



#ifdef CONFIG_ARM_MPU

struct mpu_rgn_info mpu_rgn_info;

#endif
@@ -148,9 +155,21 @@ void __init adjust_lowmem_bounds(void) 
 */

void __init paging_init(const struct machine_desc *mdesc)

{

	void *zero_page;



	early_trap_init((void *)vectors_base);

	mpu_setup();



	/* allocate the zero page. */

	zero_page = memblock_alloc(PAGE_SIZE, PAGE_SIZE);

	if (!zero_page)

		panic("%s: Failed to allocate %lu bytes align=0x%lx\n",

		      __func__, PAGE_SIZE, PAGE_SIZE);



	bootmem_init();



	empty_zero_page = virt_to_page(zero_page);

	flush_dcache_page(empty_zero_page);

}



/*