linux-kernel - RE: [PATCH v7 3/3] x86, mce: Add __mcsafe

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Date:	Wed, 6 Jan 2016 16:57:13 +0000
From:	"Luck, Tony" <tony.luck@...el.com>
To:	"Williams, Dan J" <dan.j.williams@...el.com>
CC:	Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	"Elliott, Robert (Persistent Memory)" <elliott@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux MM <linux-mm@...ck.org>,
	linux-nvdimm <linux-nvdimm@...1.01.org>, X86 ML <x86@...nel.org>
Subject: RE: [PATCH v7 3/3] x86, mce: Add __mcsafe_copy()

>> 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).

-Tony