linux-kernel - Re: [PATCH v8 3/3] x86, mce: Add __mcsafe

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Date:	Sat, 9 Jan 2016 14:33:16 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Tony Luck <tony.luck@...il.com>,
	linux-nvdimm <linux-nvdimm@...1.01.org>,
	Borislav Petkov <bp@...en8.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Robert <elliott@....com>, Ingo Molnar <mingo@...nel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH v8 3/3] x86, mce: Add __mcsafe_copy()

On Sat, Jan 9, 2016 at 2:15 PM, Dan Williams <dan.j.williams@...el.com> wrote:
> On Sat, Jan 9, 2016 at 11:39 AM, Tony Luck <tony.luck@...il.com> wrote:
>> On Sat, Jan 9, 2016 at 9:57 AM, Andy Lutomirski <luto@...capital.net> wrote:
>>> On Sat, Jan 9, 2016 at 9:48 AM, Tony Luck <tony.luck@...il.com> wrote:
>>>> ERMS?
>>>
>>> It's the fast string extension, aka Enhanced REP MOV STOS.  On CPUs
>>> with that feature (and not disabled via MSR), plain ol' rep movs is
>>> the fastest way to copy bytes.  I think this includes all Intel CPUs
>>> from SNB onwards.
>>
>> Ah ... very fast at copying .. but currently not machine check recoverable.
>
> Hmm, I assume for the pmem driver I'll want to check at runtime if the
> cpu has machine check recovery and fall back to the faster copy if
> it's not available?

Shouldn't that logic live in the mcsafe_copy routine itself rather
than being delegated to callers?

--Andy