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

On Tue, Feb 9, 2016 at 6:06 PM, Toshi Kani <toshi.kani(a)hpe.com&gt; wrote: > 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). If we're modifying crash(8) can't we also teach it to mmap /dev/pmemX directly?  With commit 90a545e98126 "restrict /dev/mem to idle io memory ranges" /dev/mem should not have access to active pmem ranges.