MIPS: Fix memory regions reaching top of physical
Memory regions added with add_memory_region() at the top of the physical address space will have their end address overflow to 0. This causes them to be rejected as invalid, and would cause various other issues later on. This causes issues on Malta and Boston platforms when wanting to use all 2GB of RAM on a 32-bit kernel, either via highmem (using physical addresses 0x90000000..0xFFFFFFFF), or with the Malta Enhanced Virtual Addressing (EVA) layout which exposes the whole 0x80000000..0xFFFFFFFF physical address range to kernel mode at 0x00000000..0x7FFFFFFF. Due to the abundance of these non-overflow assumptions and the fact that memblock already avoids the arithmetic overflow by limiting the size of new memory regions without the arch code knowing it (in particular mem_init_free_highmem() will trigger a page dump due to nonzero mapcount on the last page), it is simpler and safer to just limit the size of the region in a similar way to memblock but at the arch level to allow most of the RAM to be used without arithmetic overflows. Therefore we detect this case specifically and reduce the size of the region slightly to avoid the arithmetic overflows and cause the last page to be ignored. Signed-off-by: James Hogan <james.hogan@imgtec.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/13857/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
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@ -87,6 +87,13 @@ void __init add_memory_region(phys_addr_t start, phys_addr_t size, long type)
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int x = boot_mem_map.nr_map;
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int i;
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/*
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* If the region reaches the top of the physical address space, adjust
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* the size slightly so that (start + size) doesn't overflow
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*/
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if (start + size - 1 == (phys_addr_t)ULLONG_MAX)
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--size;
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/* Sanity check */
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if (start + size < start) {
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pr_warn("Trying to add an invalid memory region, skipped\n");
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