linux-kernel - Re: [PATCH v2 6/8] cxl/mem: Enable commands via CEL

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Date:   Thu, 11 Feb 2021 12:34:35 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Ben Widawsky <ben.widawsky@...el.com>
Cc:     Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        linux-cxl@...r.kernel.org, Linux ACPI <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Chris Browy <cbrowy@...ry-design.com>,
        Christoph Hellwig <hch@...radead.org>,
        David Hildenbrand <david@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Jon Masters <jcm@...masters.org>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vishal Verma <vishal.l.verma@...el.com>,
        "John Groves (jgroves)" <jgroves@...ron.com>,
        "Kelley, Sean V" <sean.v.kelley@...el.com>
Subject: Re: [PATCH v2 6/8] cxl/mem: Enable commands via CEL

On Thu, Feb 11, 2021 at 9:45 AM Ben Widawsky <ben.widawsky@...el.com> wrote:
[..]
> > > +   if (mbox_cmd.size_out > sizeof(gsl)) {
> > > +           dev_warn(dev, "%zu excess logs\n",
> > > +                    (mbox_cmd.size_out - sizeof(gsl)) /
> > > +                            sizeof(struct gsl_entry));
> >
> > This could well happen given spec seems to allow for other
> > entries defined by other specs.
>
> Interesting. When I read the spec before (multiple times) I was certain it said
> other UUIDs aren't allowed. You're correct though that the way it is worded,
> this is a bad check. AIUI, the spec permits any UUID and as such I think we
> should remove tainting for unknown UUIDs. Let me put the exact words:
>
> Table 169 & 170
> "Log Identifier: UUID representing the log to retrieve data for. The following
>  Log Identifier UUIDs are defined in this specification"
>
> To me this implies UUIDs from other (not "this") specifications are permitted.
>
> Dan, I'd like your opinion here. I'm tempted to change the current WARN to a
> dev_dbg or somesuch.

Yeah, sounds ok, and the command is well defined to be a read-only,
zero-side-effect affair. If a vendor did really want to sneak in a
proprietary protocol over this interface it would be quite awkward.