Re: [PATCH] x86/mm: Add x86 valid_phys_addr_range() for /dev/mem

x86 does not define ARCH_HAS_VALID_PHYS_ADDR_RANGE, which leads /dev/mem to use the default valid_phys_addr_range() and valid_mmap_phys_addr_range() in drivers/char/mem.c. The default valid_phys_addr_range() allows any range lower than __pa(high_memory), which is the end of system RAM, and disallows any range higher than it. Persistent memory may be located at lower and/or higher address of __pa(high_memory) depending on their memory slots. When using crash(8) via /dev/mem for analyzing data in persistent memory, it can only access to the one lower than __pa(high_memory). Add x86 valid_phys_addr_range() and valid_mmap_phys_addr_range() to provide better checking: - Physical address range is valid when it is fully backed by IORESOURCE_MEM, regardless of __pa(high_memory). - Other ranges, including holes, are invalid. This also allows crash(8) to access persistent memory ranges via /dev/mem (with a minor change to remove high_memory check from crash itself).