linux-kernel - Re: [PATCH v13] x86, mce: Add memcpy

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Date:	Wed, 24 Feb 2016 11:37:09 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Tony Luck <tony.luck@...il.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v13] x86, mce: Add memcpy_trap()

On Wed, Feb 24, 2016 at 11:27 AM, Tony Luck <tony.luck@...il.com> wrote:
>
> This isn't just about NVDIMMs. It is about uncorrected errors in any
> type of memory.
>
> The copy_from_user() case I'd like to fix is when there is an
> uncorrected in memory. This can happen to regular DDR3/DDR4 memory
> just as it can happen to NVDIMM. When a user process directly reads
> the location with the uncorrected error the h/w triggers a machine
> check and if the error is marked as recoverable the kernel will SIGBUS
> the process. See mm/memory-failure.c

But the way to fix that is absolutely *not* to introduce some new concept.

You'd just extend the _existing_ get_user() and put_user() functions
to return a different error code for a memory error. Instead of
-EFAULT, maybe they can return -EMEMERR or something.

I do not see how it could possibly ever make sense to introduce a new
name and then make old users use that new name instead.

                        Linus