linux-kernel - Re: [PATCH v2 4/4] acpi/ghes, cxl/pci: Trace FW-First CXL Protocol Errors

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Message-ID: <66fde27512fa2_964f22945e@dwillia2-xfh.jf.intel.com.notmuch>
Date: Wed, 2 Oct 2024 17:16:53 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>,
	<linux-efi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-cxl@...r.kernel.org>
CC: Ard Biesheuvel <ardb@...nel.org>, Alison Schofield
	<alison.schofield@...el.com>, Vishal Verma <vishal.l.verma@...el.com>, "Ira
 Weiny" <ira.weiny@...el.com>, Dan Williams <dan.j.williams@...el.com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>, Yazen Ghannam
	<yazen.ghannam@....com>, Bowman Terry <terry.bowman@....com>
Subject: Re: [PATCH v2 4/4] acpi/ghes, cxl/pci: Trace FW-First CXL Protocol
 Errors

Smita Koralahalli wrote:
> When PCIe AER is in FW-First, OS should process CXL Protocol errors from
> CPER records.
> 
> Reuse the existing work queue cxl_cper_work registered with GHES to notify
> the CXL subsystem on a Protocol error.
> 
> The defined trace events cxl_aer_uncorrectable_error and
> cxl_aer_correctable_error currently trace native CXL AER errors. Reuse
> them to trace FW-First Protocol Errors.
> 
> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
> ---
> v2:
> 	Removed pr_warn for serial number.
> 	p_err -> rec/p_rec.
> ---
>  drivers/acpi/apei/ghes.c | 14 ++++++++++++++
>  drivers/cxl/core/pci.c   | 24 ++++++++++++++++++++++++
>  drivers/cxl/cxlpci.h     |  3 +++
>  drivers/cxl/pci.c        | 20 ++++++++++++++++++--
>  include/cxl/event.h      |  1 +
>  5 files changed, 60 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
> index 9dcf0f78458f..5082885e1f2c 100644
> --- a/drivers/acpi/apei/ghes.c
> +++ b/drivers/acpi/apei/ghes.c
> @@ -723,6 +723,20 @@ static void cxl_cper_handle_prot_err(struct acpi_hest_generic_data *gdata)
>  
>  	if (cxl_cper_handle_prot_err_info(gdata, &wd.p_rec))
>  		return;
> +
> +	guard(spinlock_irqsave)(&cxl_cper_work_lock);
> +
> +	if (!cxl_cper_work)
> +		return;
> +
> +	wd.event_type = CXL_CPER_EVENT_PROT_ERR;
> +
> +	if (!kfifo_put(&cxl_cper_fifo, wd)) {
> +		pr_err_ratelimited("CXL CPER kfifo overflow\n");
> +		return;
> +	}
> +
> +	schedule_work(cxl_cper_work);

The cxl_cper_work item is only for cases where the cxl_pci driver might care
about annotating an error report with driver specific details like the
impacted kernel object name, 'struct cxl_memdev', or address translation
for DPA data.

Protocol errors that are not endpoint errors should never be placed in
the cxl_cper_fifo. That is exclusively for errors that cxl_pci needs to
consume.

My expectation is that similar to aer_recover_queue for PCIe protocol
errors CXL needs to grow a cxl_recover_queue that at a minimum triggers
new trace events to dump these records to RAS daemon.

I am struggling to think what useful information cxl_pci could ever
append to a protocol error event.

What is more likely is that later when Terry adds port error handling a
CPER protocol error record could trigger a new cxl_do_recovery() to
react to CXL topology errors that might impact downstream CXL devices.
In that case the notification will come through something like a new
'struct cxl_error_handlers *' hanging off 'struct pci_driver' since
accelerator drivers are going to have distinct error handling from
generic memory expanders.