linux-kernel - Re: [PATCH v5 05/16] PCI/AER: Add CXL PCIe Port correctable error support in AER service driver

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Message-ID: <20250207175436.0000666b@huawei.com>
Date: Fri, 7 Feb 2025 17:54:36 +0000
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Gregory Price <gourry@...rry.net>
CC: Terry Bowman <terry.bowman@....com>, <linux-cxl@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-pci@...r.kernel.org>,
	<nifan.cxl@...il.com>, <dave@...olabs.net>, <dave.jiang@...el.com>,
	<alison.schofield@...el.com>, <vishal.l.verma@...el.com>,
	<dan.j.williams@...el.com>, <bhelgaas@...gle.com>, <mahesh@...ux.ibm.com>,
	<ira.weiny@...el.com>, <oohall@...il.com>, <Benjamin.Cheatham@....com>,
	<rrichter@....com>, <nathan.fontenot@....com>,
	<Smita.KoralahalliChannabasappa@....com>, <lukas@...ner.de>,
	<ming.li@...omail.com>, <PradeepVineshReddy.Kodamati@....com>,
	<alucerop@....com>
Subject: Re: [PATCH v5 05/16] PCI/AER: Add CXL PCIe Port correctable error
 support in AER service driver

On Thu, 6 Feb 2025 13:33:55 -0500
Gregory Price <gourry@...rry.net> wrote:

> On Tue, Jan 07, 2025 at 08:38:41AM -0600, Terry Bowman wrote:
> > The AER service driver supports handling Downstream Port Protocol Errors in
> > Restricted CXL host (RCH) mode also known as CXL1.1. It needs the same
> > functionality for CXL PCIe Ports operating in Virtual Hierarchy (VH)
> > mode.[1]
> > 
> > CXL and PCIe Protocol Error handling have different requirements that
> > necessitate a separate handling path. The AER service driver may try to
> > recover PCIe uncorrectable non-fatal errors (UCE). The same recovery is not
> > suitable for CXL PCIe Port devices because of potential for system memory
> > corruption. Instead, CXL Protocol Error handling must use a kernel panic
> > in the case of a fatal or non-fatal UCE. The AER driver's PCIe Protocol
> > Error handling does not panic the kernel in response to a UCE.
> >  
> 
> Naive question: is a panic actually required if the memory is a userland
> resource?

It's a protocol error, not a contained memory issue.
You'd need to find everything using that memory and kill it.

Maybe longer term if it's DAX and we know whole device is allocated
to only a few apps can resolve more smoothly.


> 
> The code in arch/x86/kernel/cpu/mce/core.c suggests we may not panic
> if an uncorrectable error occurs in this fashion, but simply a SIGBUS.
> 
> Unless this is down the wrong pipe - in which case disregard.
> 
> I'm still digging through background on this patch set so I may be
> barking up the wrong tree.
> 
> ~Gregory