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Date:   Thu, 23 Sep 2021 13:48:52 -0700
From:   Jane Chu <>
To:     Dan Williams <>,
        "Darrick J. Wong" <>
Cc:     Vishal L Verma <>,
        Dave Jiang <>,
        "Weiny, Ira" <>,
        Al Viro <>,
        Matthew Wilcox <>, Jan Kara <>,
        Linux NVDIMM <>,
        Linux Kernel Mailing List <>,
        linux-fsdevel <>
Subject: Re: [PATCH 0/3] dax: clear poison on the fly along pwrite

On 9/15/2021 1:27 PM, Dan Williams wrote:
>>> I'm also thinking about the MOVEDIR64B instruction and how it
>>> might be used to clear poison on the fly with a single 'store'.
>>> Of course, that means we need to figure out how to narrow down the
>>> error blast radius first.
> It turns out the MOVDIR64B error clearing idea runs into problem with
> the device poison tracking. Without the explicit notification that
> software wanted the error cleared the device may ghost report errors
> that are not there anymore. I think we should continue explicit error
> clearing and notification of the device that the error has been
> cleared (by asking the device to clear it).

Sorry for the late response, I was out for several days.

Your concern is understood.  I wasn't thinking of an out-of-band
MOVDIR64B to clear poison, I was thinking about adding a case to
pmem_clear_poison(), such that if CPUID feature shows that
MOVDIR64B is supported, instead of calling the BIOS interface
to clear poison, MOVDIR64B could be called. The advantage is
a. a lot faster; b. smaller radius.  And the driver has a chance
to update its ->bb record.


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