linux-kernel - Re: [PATCH 5/5] dax: "Hotplug" persistent memory for use like normal RAM

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Message-ID: <CAPcyv4ikXD8rJAmV6tGNiq56m_ZXPZNrYkTwOSUJ7D1O_M5s=w@mail.gmail.com>
Date:   Fri, 25 Jan 2019 09:18:41 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     "Du, Fan" <fan.du@...el.com>
Cc:     Jane Chu <jane.chu@...cle.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Michal Hocko <mhocko@...e.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Takashi Iwai <tiwai@...e.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Jér?me Glisse <jglisse@...hat.com>,
        Borislav Petkov <bp@...e.de>,
        Yaowei Bai <baiyaowei@...s.chinamobile.com>,
        Ross Zwisler <zwisler@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Wu, Fengguang" <fengguang.wu@...el.com>
Subject: Re: [PATCH 5/5] dax: "Hotplug" persistent memory for use like normal RAM

On Fri, Jan 25, 2019 at 12:20 AM Du, Fan <fan.du@...el.com> wrote:
>
> 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?

The common RAS workflow always kicks in, it's just the page state
presented by a DAX mapping needs distinct handling. Once it is
hot-plugged it no longer needs to be treated differently than "System
RAM".

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

The hotplug effectively disconnects this address range from the ARS
results. They will still be reported in the libnvdimm "region" level
badblocks instance, but there's no safe / coordinated way to go clear
those errors without additional kernel enabling. There is no "clear
error" semantic for "System RAM".