linux-kernel - Re: [PATCH 2/3] cxl/mbox: Add GET_POISON

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Message-ID: <20220616214740.7pyjagx3gosni7mw@offworld>
Date:   Thu, 16 Jun 2022 14:47:40 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Alison Schofield <alison.schofield@...el.com>
Cc:     "Williams, Dan J" <dan.j.williams@...el.com>,
        "Weiny, Ira" <ira.weiny@...el.com>,
        "Verma, Vishal L" <vishal.l.verma@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        "linux-cxl@...r.kernel.org" <linux-cxl@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "a.manzanares@...sung.com" <a.manzanares@...sung.com>
Subject: Re: [PATCH 2/3] cxl/mbox: Add GET_POISON_LIST mailbox command support

On Thu, 16 Jun 2022, Alison Schofield wrote:
>I'm headed in this direction -

I like these interfaces, btw.

>cxl list --media-errors -m mem1
>	lists media errors for requested memdev

But in this patchset you're only listing for persistent configurations.
So if there is a volatile partion, or the whole device is volatile,
this would not consider that.

So unless I'm missing something, we need to consider ram_range as well.

>cxl list --media-errors -r region#
>	lists region errors with HPA addresses
>	(So here cxl tool will collect the poison for all the regions
>	 memdevs and do the DPA to HPA translation)

I was indeed thinking along these lines. But similar to the above,
the region driver also has plans to enumarate volatile regions
configured by BIOS.

>
>To answer your question, I wasn't thinking of limiting
>the range within the memdev, but certainly could. And if we were
>taking in ranges, those ranges would need to be checked.

My question was originally considering poisoning only within pmem DPA
ranges, but now I'm wondering if all this also applies equally to volatile
parts as well... Reading the spec I interpret both, but reading the
T3 Memory Device Software Guide '2.13.19' it only mentions persistent
capacity.

>
>$cxl list --media-errors -m mem1 --range-start=  --range-end|len=

I figure this kind of like the above with regions being very arbitrary
and dynamic.

>Now, if I left the sysfs interface as is, the driver will read the
>entire poison list for the memdev and then cxl tool will filter it
>for the range requested.
>
>Or, maybe we should implement in libcxl (not sysfs), with memdev and
>range options and only collect from the device the range requested.

I wonder if the latter may be the better option considering that always
scanning the entire memdev would cause unnecessary media scan wait times,
specially for large capacities.

Thanks,
Davidlohr