linux-kernel - Re: [PATCH] cxl/pci: Change CXL AER support check to use native AER

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Message-ID: <65441103b3b1b_44d229485@dwillia2-xfh.jf.intel.com.notmuch>
Date:   Thu, 2 Nov 2023 14:13:39 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Alison Schofield <alison.schofield@...el.com>,
        Terry Bowman <terry.bowman@....com>
CC:     <vishal.l.verma@...el.com>, <ira.weiny@...el.com>,
        <bwidawsk@...nel.org>, <dan.j.williams@...el.com>,
        <dave.jiang@...el.com>, <Jonathan.Cameron@...wei.com>,
        <linux-cxl@...r.kernel.org>,
        <Smita.KoralahalliChannabasappa@....com>, <rrichter@....com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cxl/pci: Change CXL AER support check to use native AER

Alison Schofield wrote:
> On Thu, Nov 02, 2023 at 10:52:32AM -0500, Terry Bowman wrote:
> > Native CXL protocol errors are delivered to the OS through AER
> > reporting. The owner of AER owns CXL Protocol error management with
> > respect to _OSC negotiation.[1] CXL device errors are handled by a
> > separate interrupt with native control gated by _OSC control field
> > 'CXL Memory Error Reporting Control'.
> > 
> > The CXL driver incorrectly checks for 'CXL Memory Error Reporting
> > Control' before accessing AER registers and caching RCH downport
> > AER registers. Replace the current check in these 2 cases with
> > native AER checks.
> 
> Hi Terry,  Does this have a user visible impact? 

Saw this after I applied it. It is good feedback in general.

The reason I did not ask for this clarification was that this is fixing
brand new code and was just using the wrong flag, so I had the context.
A backporter will never need to make a judgement call about this patch.

The end user impact is that CXL protocol errors that could be handled by
AER will not be handled if Linux failed to negotiate memory error
handling. Memory errors are strictly related to memory-error-record
events, not protocol errors.