linux-kernel - Re: [PATCH v14] x86, mce: Add memcpy

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Message-ID: <20160302204739.GA4728@intel.com>
Date:	Wed, 2 Mar 2016 12:47:41 -0800
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tony Luck <tony.luck@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH v14] x86, mce: Add memcpy_mcsafe()

On Thu, Feb 18, 2016 at 11:47:26AM -0800, Tony Luck wrote:
> Make use of the EXTABLE_FAULT exception table entries to write
> a kernel copy routine that doesn't crash the system if it
> encounters a machine check. Prime use case for this is to copy
> from large arrays of non-volatile memory used as storage.
> 
> We have to use an unrolled copy loop for now because current
> hardware implementations treat a machine check in "rep mov"
> as fatal. When that is fixed we can simplify.

Ping.

Anything more needed for this?  In his last message Linus
seemed OK with a *kernel* copy function that avoided death
by machine check.  He said:

   What a "memcpy_fault()" (or whatever it would be called) means is
   that the kernel is doing its own copies, but knows that there is some
   fragility involved, and wants to have a recovery mechanism that isn't
   "oops, we got a machine check in the kernel, now we need to kill the
   machine".

The only things left to argue are the name, and the return value.

-Tony