RE: [PATCH v3] x86/mce: retrieve poison range from hardware

[Dan Williams]

Luck, Tony wrote:
> +m.misc = (MCI_MISC_ADDR_PHYS << 6) | __ffs64(mem_err->physical_addr_mask);
> 
> Do we want to unconditionally trust the sanity of the BIOS provided physical_address_mask?
> 
> There's a warning comment on the kernel __ffs64() function:
> 
>  * The result is not defined if no bits are set, so check that @word
>  * is non-zero before calling this.
> 
> Otherwise, this looks like a good idea.

It appears the kernel is trusting that ->physical_addr_mask is non-zero
in other paths. So this is at least equally broken in the presence of a
broken BIOS. The impact is potentially larger though with this change,
so it might be a good follow-on patch to make sure that
->physical_addr_mask gets fixed up to a minimum mask value.