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

[Dan Williams]

On Tue, Feb 9, 2016 at 6:06 PM, Toshi Kani <toshi.kani@xxxxxxx> 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.