Re: [PATCH V2 2/2] x86: add phys addr validity check for /dev/mem mmap

[Dave Hansen <dave.hansen@intel.com>]

On 08/15/2014 04:44 AM, Frantisek Hrbata wrote:
> +int valid_phys_addr_range(phys_addr_t addr, size_t count)
> +{
> +	return addr + count <= __pa(high_memory);
> +}
> +
> +int valid_mmap_phys_addr_range(unsigned long pfn, size_t count)
> +{
> +	return arch_pfn_possible(pfn + (count >> PAGE_SHIFT));
> +}

It definitely fixes the issue as you described it.

It's a bit unfortunate that the highmem check isn't tied in to the
_existing_ /dev/mem limitations in some way, but it's not a deal breaker
for me.

The only other thing is to make sure this doesn't add some limitation to
64-bit where we can't map things above the end of memory (end of memory
== high_memory on 64-bit).  As long as you've done this, I can't see a
downside.