Re: [PATCH 0/3] dax: clear poison on the fly along pwrite

[Jane Chu]

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.

thanks,
-jane