Re: [PATCH v7 3/3] x86, mce: Add __mcsafe_copy()

[Dan Williams <dan.j.williams@intel.com>]

On Wed, Jan 6, 2016 at 8:57 AM, Luck, Tony <tony.luck@intel.com> wrote:
>>> I do select it, but by randconfig I still need to handle the
>>> CONFIG_X86_MCE=n case.
>>>
>>>> I'm seriously wondering whether the ifdef still makes sense. Now I don't have an extra exception table and routines to sort/search/fixup, it doesn't seem as useful as it was a few iterations ago.
>>>
>>> Either way is ok with me.  That said, the extra definitions to allow
>>> it compile out when not enabled don't seem too onerous.
>>
>> This works for me, because all we need is the definitions.  As long as
>> we don't attempt to link to mcsafe_copy() we get the benefit of
>> compiling this out when de-selected:
>
> It seems  that Kconfig's "select" statement doesn't auto-select other things
> that are dependencies of the symbol you choose.
>
> CONFIG_MCE_KERNEL_RECOVERY really is dependent on
> CONFIG_X86_MCE ... having the code for the __mcsafe_copy()
> linked into the kernel won't do you any good without a machine
> check handler that jumps to the fixup code.
>
> So I think you have to select X86_MCE as well (or Kconfig needs
> to be taught to do it automatically ... but I have a nagging feeling
> that this is known behavior).
>

I don't want to force it on, otherwise we might as well remove the
ability to configure it.  Instead I have this:

config BLK_DEV_PMEM
       select MCE_KERNEL_RECOVERY if X86_MCE && X86_64

...that way if you turn on X86_MCE and BLK_DEV_PMEM you get
MCE_KERNEL_RECOVERY by default.

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