RE: [PATCH 5/5] dax: "Hotplug" persistent memory for use like normal RAM

[Du, Fan]

Dan

Thanks for the insights!

Can I say, the UCE is delivered from h/w to OS in a single way in case of machine
check, only PMEM/DAX stuff filter out UC address and managed in its own way by
badblocks, if PMEM/DAX doesn't do so, then common RAS workflow will kick in,
right?

And how about when ARS is involved but no machine check fired for the function
of this patchset?

>-----Original Message-----
>From: Linux-nvdimm [mailto:linux-nvdimm-bounces@xxxxxxxxxxxx] On Behalf
>Of Dan Williams
>Sent: Friday, January 25, 2019 2:28 PM
>To: Jane Chu <jane.chu@xxxxxxxxxx>
>Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>; Michal Hocko
><mhocko@xxxxxxxx>; linux-nvdimm <linux-nvdimm@xxxxxxxxxxxx>; Takashi
>Iwai <tiwai@xxxxxxx>; Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>; Huang,
>Ying <ying.huang@xxxxxxxxx>; Linux Kernel Mailing List
><linux-kernel@xxxxxxxxxxxxxxx>; Linux MM <linux-mm@xxxxxxxxx>; Jérôme
>Glisse <jglisse@xxxxxxxxxx>; Borislav Petkov <bp@xxxxxxx>; Yaowei Bai
><baiyaowei@xxxxxxxxxxxxxxxxxxxx>; Ross Zwisler <zwisler@xxxxxxxxxx>;
>Bjorn Helgaas <bhelgaas@xxxxxxxxxx>; Andrew Morton
><akpm@xxxxxxxxxxxxxxxxxxxx>; Wu, Fengguang <fengguang.wu@xxxxxxxxx>
>Subject: Re: [PATCH 5/5] dax: "Hotplug" persistent memory for use like
>normal RAM
>
>On Thu, Jan 24, 2019 at 10:13 PM Jane Chu <jane.chu@xxxxxxxxxx> wrote:
>>
>> Hi, Dave,
>>
>> While chatting with my colleague Erwin about the patchset, it occurred
>> that we're not clear about the error handling part. Specifically,
>>
>> 1. If an uncorrectable error is detected during a 'load' in the hot
>> plugged pmem region, how will the error be handled?  will it be
>> handled like PMEM or DRAM?
>
>DRAM.
>
>> 2. If a poison is set, and is persistent, which entity should clear
>> the poison, and badblock(if applicable)? If it's user's responsibility,
>> does ndctl support the clearing in this mode?
>
>With persistent memory advertised via a static logical-to-physical
>storage/dax device mapping, once an error develops it destroys a
>physical *and* logical part of a device address space. That loss of
>logical address space makes error clearing a necessity. However, with
>the DRAM / "System RAM" error handling model, the OS can just offline
>the page and map a different one to repair the logical address space.
>So, no, ndctl will not have explicit enabling to clear volatile
>errors, the OS will just dynamically offline problematic pages.
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