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

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Message-ID: <CALCETrVY7407jf-o4n1ZjKu=QNfUv9fnbxDQwX8Sa=o4PY+aFA@mail.gmail.com>
Date:	Sun, 27 Dec 2015 05:25:45 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Boris Petkov <bp@...en8.de>
Cc:	Tony Luck <tony.luck@...il.com>,
	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 5:17 AM, Boris Petkov <bp@...en8.de> wrote:
> Andy Lutomirski <luto@...capital.net> wrote:
>>You certainly can, but it doesn't scale well to multiple users of
>>similar mechanisms.  It also prevents you from using the same
>>mechanism in anything that could be inlined, which is IMO kind of
>>unfortunate.
>
> Well, but the bit 31 game doesn't make it any better than the bit 63 fun IMO. Should the exception table entry maybe grow a u32 flags instead?
>

That could significantly bloat the kernel image.

Anyway, the bit 31 game isn't so bad IMO because it's localized to the
extable macros and the extable reader, whereas the bit 63 thing is all
tangled up with the __mcsafe_copy thing, and that's just the first
user of a more general mechanism.

Did you see this:

https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/commit/?h=strict_uaccess_fixups/patch_v1&id=16644d9460fc6531456cf510d5efc57f89e5cd34

(If you and/or Tony use it, take out the uaccess stuff -- it's not
useful for what you're doing, and I should have stuck that in a
separate patch in the first place.)

--Andy
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