Re: [PATCH 0/4] Adding support to parse BERT for libnvdimm

From: "Kani, Toshi" <toshi.kani@hpe.com>
To: "dan.j.williams@intel.com" <dan.j.williams@intel.com>
Cc: "tony.luck@intel.com" <tony.luck@intel.com>,
	"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
	"rjw@rjwysocki.net" <rjw@rjwysocki.net>,
	"linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
	"lenb@kernel.org" <lenb@kernel.org>
Subject: Re: [PATCH 0/4] Adding support to parse BERT for libnvdimm
Date: Fri, 30 Mar 2018 16:45:58 +0000	[thread overview]
Message-ID: <1522428337.2693.271.camel@hpe.com> (raw)
In-Reply-To: <CAPcyv4iBnOLrFyhZBpAhkrdkY42w7g125jQhxi2Qv6drC7HQdA@mail.gmail.com>

On Fri, 2018-03-30 at 09:38 -0700, Dan Williams wrote:
> On Fri, Mar 30, 2018 at 8:04 AM, Kani, Toshi <toshi.kani@hpe.com> wrote:
> > On Thu, 2018-03-29 at 15:37 -0700, Dave Jiang wrote:
> > > The following series implements support for parsing of the BERT records
> > > and adding the error memory ranges to nvdimm badblocks in order for the
> > > kernel to avoid prevent the kernel from accessing those areas. And with
> > > the addition of this support, we can surface the nd regions instead of waiting
> > > for ARS to complete. So the ARS handling is reworked to run in the
> > > background and not block nd region registration.
> > 
> > Hi Dave,
> > 
> > I agree on the problem, and adding an ability to obtain pmem badblocks
> > records at boot-time without waiting for a new ARS scan to complete is a
> > good option for users.
> > 
> > However, I do not think using the BERT table is a good approach.  This
> > requires FW to report pmem badblocks records with a new interface in
> > addition to ARS records, which FW already implements for pmem.  ACPI 6.2
> > defines Start ARS with Flags Bit[1] set to report badblocks record
> > without starting a new ARS scan.  We set this bit after receiving a 0x81
> > notification at this point.
> > 
> > Can we use ARS with Flags bit[1] set at boot-time so that both OS and FW
> > can use the same ARS implementation?
> 
> You have a point.
> 
> The other benefit I see to this policy is that it hopefully convinces
> BIOS implementations to not run ARS at boot and leave it to the OS to
> manage it in the background. If the platform has any critical errors
> to report, i.e. ones that triggered a system reset, then it should be
> able to report them in the flag-bit1 case.

Agreed.

> This also lets the implementation be completely self contained to the
> nfit driver, and not grow any BERT entanglements that may or may not
> be valid for the persistent memory case.

Right.  Thanks Dan!
-Toshi
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