linux-kernel - Re: [PATCHV5 3/3] x86, ras: Add __mcsafe_copy() function to recover from machine checks

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Date:	Wed, 30 Dec 2015 15:32:30 -0800
From:	Tony Luck <tony.luck@...il.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Borislav Petkov <bp@...en8.de>,
	linux-nvdimm <linux-nvdimm@...1.01.org>, X86 ML <x86@...nel.org>,
	"elliott@....com" <elliott@....com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Williams, Dan J" <dan.j.williams@...el.com>,
	Ingo Molnar <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHV5 3/3] x86, ras: Add __mcsafe_copy() function to recover
 from machine checks

On Sun, Dec 27, 2015 at 4:18 AM, Andy Lutomirski <luto@...capital.net> wrote:
> I think I can save you some pondering.  This old patch gives two flag
> bits.  Feel free to borrow the patch, but you'll probably want to
> change the _EXTABLE_CLASS_XYZ macros:
>
> https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/commit/?h=strict_uaccess_fixups/patch_v1&id=16644d9460fc6531456cf510d5efc57f89e5cd34

Thanks!

I took that, and some of Boris's changes, and stirred it altogether at:

git://git.kernel.org/pub/scm/linux/kernel/git/ras/ras.git mcsafev6

First commit is just your patch from above (patch wouldn't apply it
directly because of other nearby changes, but I think I didn't break
it)

Second commit pulls the core of fixup_exception() into separate
functions for each class

Third adds a new class that provides the fault number to the fixup
code in regs->ax.

Fourth is just a jumble of the rest .. needs to be split into two
parts (one for machine check handler, second to add __mcsafe_copy())

Fifth is just a hack because I clearly didn't understand what I was
doing in parts 2&3 because my new class shows up as '3' not '1'!

Andy: Can you explain the assembler/linker arithmetic for the class?

-Tony
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