linux-kernel - Re: [Linux-nvdimm] [PATCH 0/2] e820: Fix handling of NvDIMM chips

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Date:	Wed, 18 Feb 2015 10:15:32 -0800
From:	Dan Williams <dan.j.williams@...el.com>
To:	Boaz Harrosh <boaz@...xistor.com>
Cc:	Matthew Wilcox <willy@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>, x86@...nel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"Roger C. Pao" <rcpao.enmotus@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-nvdimm <linux-nvdimm@...ts.01.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [Linux-nvdimm] [PATCH 0/2] e820: Fix handling of NvDIMM chips

On Tue, Feb 17, 2015 at 12:42 AM, Boaz Harrosh <boaz@...xistor.com> wrote:
> On 02/17/2015 12:03 AM, Matthew Wilcox wrote:
>> On Mon, Feb 16, 2015 at 01:07:07PM +0200, Boaz Harrosh wrote:
>>> In any way this is a problem for the new type-12 NvDIMM memory chips that
>>> are circulating around. (It is estimated that there are already 100ds of
>>> thousands NvDIMM chips in active use)
>>
>> Hang on.  NV-DIMM chips don't know anyhing about E820 tables.  They don't
>> have anything in them that says "I am type 12!".  How they are reported
>> is up to the BIOS.  Just because your BIOS vendor has chosen to report
>> tham as type 12 doesn't mean that any other BIOS vedor is going to have
>> done the same thing.
>>
>> Fortunately, the BIOS people have all got together and decided what
>> they're going to do, and it's not type 12.  Unfortunately, I think
>> I'm bound by various agreements to not say what they are going to do
>> until they do.  But putting this temporary workaround in the kernel to
>> accomodate one BIOS vendor's unreleased experimental code seems like
>> entirely the wrong idea.
>>
>
> I had a feeling I'm entering an holy war ;-).
>
> I hope you are OK with my first patch. That an unknown type need not
> be reported busy, and behave same as "reserved"?

No, it seems the safe thing to do is prevent the kernel from accessing
any memory that it does not know the side-effects of accessing.

> Then if we agree about PATCH-1, which is the actual fix.
> Then the 2nd patch (hence the RFC btw) is nothing more than
> a name.
>
> I have an old BIOS that knows nothing of NvDIMM, actually a few
> of them they all report 12.
> The fact of the matter is that all the people I've talked with,
> reported that different vendor chips, all came up type-12.
> Perhaps type-12 just means "Unknown to current BIOS"
>
> What is the name you suggest "type-12" "unknown-12".
> Do you understand why they all come out 12 ?
>

In fact it was originally "type-6" until ACPI 5 claimed that number
for official use, so these platforms, with early proof-of-concept
nvdimm support, have already gone through one transition to a new
number.  They need to do the same once an official number for nvdimm
support is published.

Put another way, these early platforms are already using out-of-tree
patches for nvdimm enabling.  They can continue to do so, or switch to
standard methods when the standard is published.
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