diff options
author | Giulio Benetti <giulio.benetti@benettiengineering.com> | 2022-11-04 23:46:18 +0300 |
---|---|---|
committer | Russell King (Oracle) <rmk+kernel@armlinux.org.uk> | 2022-11-07 17:16:44 +0300 |
commit | 340a982825f76f1cff0daa605970fe47321b5ee7 (patch) | |
tree | cdf55efdf516d84ac2fdee2bb6b1b9a7b2834916 /arch/arm/mm/nommu.c | |
parent | 612695bccfdbd52004551308a55bae410e7cd22f (diff) | |
download | linux-340a982825f76f1cff0daa605970fe47321b5ee7.tar.xz |
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 dc068f462179 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: Giulio Benetti <giulio.benetti@benettiengineering.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Diffstat (limited to 'arch/arm/mm/nommu.c')
-rw-r--r-- | arch/arm/mm/nommu.c | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/arch/arm/mm/nommu.c b/arch/arm/mm/nommu.c index c42debaded95..c1494a4dee25 100644 --- a/arch/arm/mm/nommu.c +++ b/arch/arm/mm/nommu.c @@ -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); } /* |