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mips: Fix max_mapnr being uninitialized on early stages

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[ Upstream commit e1a9ae4573 ]

max_mapnr variable is utilized in the pfn_valid() method in order to
determine the upper PFN space boundary. Having it uninitialized
effectively makes any PFN passed to that method invalid. That in its turn
causes the kernel mm-subsystem occasion malfunctions even after the
max_mapnr variable is actually properly updated. For instance,
pfn_valid() is called in the init_unavailable_range() method in the
framework of the calls-chain on MIPS:
setup_arch()
+-> paging_init()
    +-> free_area_init()
        +-> memmap_init()
            +-> memmap_init_zone_range()
                +-> init_unavailable_range()

Since pfn_valid() always returns "false" value before max_mapnr is
initialized in the mem_init() method, any flatmem page-holes will be left
in the poisoned/uninitialized state including the IO-memory pages. Thus
any further attempts to map/remap the IO-memory by using MMU may fail.
In particular it happened in my case on attempt to map the SRAM region.
The kernel bootup procedure just crashed on the unhandled unaligned access
bug raised in the __update_cache() method:

> Unhandled kernel unaligned access[#1]:
> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.7.0-rc1-XXX-dirty #2056
> ...
> Call Trace:
> [<8011ef9c>] __update_cache+0x88/0x1bc
> [<80385944>] ioremap_page_range+0x110/0x2a4
> [<80126948>] ioremap_prot+0x17c/0x1f4
> [<80711b80>] __devm_ioremap+0x8c/0x120
> [<80711e0c>] __devm_ioremap_resource+0xf4/0x218
> [<808bf244>] sram_probe+0x4f4/0x930
> [<80889d20>] platform_probe+0x68/0xec
> ...

Let's fix the problem by initializing the max_mapnr variable as soon as
the required data is available. In particular it can be done right in the
paging_init() method before free_area_init() is called since all the PFN
zone boundaries have already been calculated by that time.

Cc: stable@vger.kernel.org
Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Serge Semin 2023-12-02 14:14:20 +03:00 committed by Greg Kroah-Hartman
parent 41a4bd51d8
commit e0d2eeec88
1 changed files with 5 additions and 10 deletions
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15
arch/mips/mm/init.c
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@ -421,7 +421,12 @@ void __init paging_init(void)
(highend_pfn - max_low_pfn) << (PAGE_SHIFT - 10));
max_zone_pfns[ZONE_HIGHMEM] = max_low_pfn;
}
max_mapnr = highend_pfn ? highend_pfn : max_low_pfn;
#else
max_mapnr = max_low_pfn;
#endif
high_memory = (void *) __va(max_low_pfn << PAGE_SHIFT);
free_area_init(max_zone_pfns);
}
@ -457,16 +462,6 @@ void __init mem_init(void)
*/
BUILD_BUG_ON(IS_ENABLED(CONFIG_32BIT) && (_PFN_SHIFT > PAGE_SHIFT));
#ifdef CONFIG_HIGHMEM
#ifdef CONFIG_DISCONTIGMEM
#error "CONFIG_HIGHMEM and CONFIG_DISCONTIGMEM dont work together yet"
#endif
max_mapnr = highend_pfn ? highend_pfn : max_low_pfn;
#else
max_mapnr = max_low_pfn;
#endif
high_memory = (void *) __va(max_low_pfn << PAGE_SHIFT);
maar_init();
memblock_free_all();
setup_zero_pages(); /* Setup zeroed pages. */