5.15-stable review patch. If anyone has any objections, please let me know.
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From: Serge Semin fancer.lancer@gmail.com
[ Upstream commit 0f5cc249ff73552d3bd864e62f85841dafaa107d ]
max_low_pfn variable is incorrectly adjusted if the kernel is built with high memory support and the later is detected in a running system, so the memory which actually can be directly mapped is getting into the highmem zone. See the ZONE_NORMAL range on my MIPS32r5 system:
Zone ranges: DMA [mem 0x0000000000000000-0x0000000000ffffff] Normal [mem 0x0000000001000000-0x0000000007ffffff] HighMem [mem 0x0000000008000000-0x000000020fffffff]
while the zones are supposed to look as follows:
Zone ranges: DMA [mem 0x0000000000000000-0x0000000000ffffff] Normal [mem 0x0000000001000000-0x000000001fffffff] HighMem [mem 0x0000000020000000-0x000000020fffffff]
Even though the physical memory within the range [0x08000000;0x20000000] belongs to MMIO on our system, we don't really want it to be considered as high memory since on MIPS32 that range still can be directly mapped.
Note there might be other problems caused by the max_low_pfn variable misconfiguration. For instance high_memory variable is initialize with virtual address corresponding to the max_low_pfn PFN, and by design it must define the upper bound on direct map memory, then end of the normal zone. That in its turn potentially may cause problems in accessing the memory by means of the /dev/mem and /dev/kmem devices.
Let's fix the discovered misconfiguration then. It turns out the commit a94e4f24ec83 ("MIPS: init: Drop boot_mem_map") didn't introduce the max_low_pfn adjustment quite correct. If the kernel is built with high memory support and the system is equipped with high memory, the max_low_pfn variable will need to be initialized with PFN of the most upper directly reachable memory address so the zone normal would be correctly setup. On MIPS that PFN corresponds to PFN_DOWN(HIGHMEM_START). If the system is built with no high memory support and one is detected in the running system, we'll just need to adjust the max_pfn variable to discard the found high memory from the system and leave the max_low_pfn as is, since the later will be less than PFN_DOWN(HIGHMEM_START) anyway by design of the for_each_memblock() loop performed a bit early in the bootmem_init() method.
Fixes: a94e4f24ec83 ("MIPS: init: Drop boot_mem_map") 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 --- arch/mips/kernel/setup.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c index 145f905fb362..9d53498682d2 100644 --- a/arch/mips/kernel/setup.c +++ b/arch/mips/kernel/setup.c @@ -324,11 +324,11 @@ static void __init bootmem_init(void) panic("Incorrect memory mapping !!!");
if (max_pfn > PFN_DOWN(HIGHMEM_START)) { + max_low_pfn = PFN_DOWN(HIGHMEM_START); #ifdef CONFIG_HIGHMEM - highstart_pfn = PFN_DOWN(HIGHMEM_START); + highstart_pfn = max_low_pfn; highend_pfn = max_pfn; #else - max_low_pfn = PFN_DOWN(HIGHMEM_START); max_pfn = max_low_pfn; #endif }