linux-kernel - Re: [PATCH V2 03/11] cxl/mem: Implement Clear Event Records command

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Date:   Thu, 1 Dec 2022 13:26:18 +0000
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     <ira.weiny@...el.com>
CC:     Dan Williams <dan.j.williams@...el.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        "Ben Widawsky" <bwidawsk@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Dave Jiang <dave.jiang@...el.com>,
        <linux-kernel@...r.kernel.org>, <linux-cxl@...r.kernel.org>
Subject: Re: [PATCH V2 03/11] cxl/mem: Implement Clear Event Records command

On Wed, 30 Nov 2022 16:27:11 -0800
ira.weiny@...el.com wrote:

> From: Ira Weiny <ira.weiny@...el.com>
> 
> CXL rev 3.0 section 8.2.9.2.3 defines the Clear Event Records mailbox
> command.  After an event record is read it needs to be cleared from the
> event log.
> 
> Implement cxl_clear_event_record() to clear all record retrieved from
> the device.
> 
> Each record is cleared explicitly.  A clear all bit is specified but
> events could arrive between a get and any final clear all operation.
> This means events would be missed.
> Therefore each event is cleared specifically.
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
I think there is a type issue on the min_t() calculation with that addressed
this looks good to me.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>

> 
> ---
> Changes from V1:
> 	Clear Event Record allows for u8 handles while Get Event Record
> 	allows for u16 records to be returned.  Based on Jonathan's
> 	feedback; allow for all event records to be handled in this
> 	clear.  Which means a double loop with potentially multiple
> 	Clear Event payloads being sent to clear all events sent.
> 
> Changes from RFC:
> 	Jonathan
> 		Clean up init of payload and use return code.
> 		Also report any error to clear the event.
> 		s/v3.0/rev 3.0
> ---
>  drivers/cxl/core/mbox.c      | 61 +++++++++++++++++++++++++++++++-----
>  drivers/cxl/cxlmem.h         | 14 +++++++++
>  include/uapi/linux/cxl_mem.h |  1 +
>  3 files changed, 69 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
> index 70b681027a3d..076a3df0ba38 100644
> --- a/drivers/cxl/core/mbox.c
> +++ b/drivers/cxl/core/mbox.c
> @@ -52,6 +52,7 @@ static struct cxl_mem_command cxl_mem_commands[CXL_MEM_COMMAND_ID_MAX] = {
>  #endif
>  	CXL_CMD(GET_SUPPORTED_LOGS, 0, CXL_VARIABLE_PAYLOAD, CXL_CMD_FLAG_FORCE_ENABLE),
>  	CXL_CMD(GET_EVENT_RECORD, 1, CXL_VARIABLE_PAYLOAD, 0),
> +	CXL_CMD(CLEAR_EVENT_RECORD, CXL_VARIABLE_PAYLOAD, 0, 0),
>  	CXL_CMD(GET_FW_INFO, 0, 0x50, 0),
>  	CXL_CMD(GET_PARTITION_INFO, 0, 0x20, 0),
>  	CXL_CMD(GET_LSA, 0x8, CXL_VARIABLE_PAYLOAD, 0),
> @@ -708,6 +709,42 @@ int cxl_enumerate_cmds(struct cxl_dev_state *cxlds)
>  }
>  EXPORT_SYMBOL_NS_GPL(cxl_enumerate_cmds, CXL);
>  
> +static int cxl_clear_event_record(struct cxl_dev_state *cxlds,
> +				  enum cxl_event_log_type log,
> +				  struct cxl_get_event_payload *get_pl,
> +				  u16 total)
> +{
> +	struct cxl_mbox_clear_event_payload payload = {
> +		.event_log = log,
> +	};
> +	int cnt;
> +
> +	/*
> +	 * Clear Event Records uses u8 for the handle cnt while Get Event
> +	 * Record can return up to 0xffff records.
> +	 */
> +	for (cnt = 0; cnt < total; /* cnt incremented internally */) {
> +		u8 nr_recs = min_t(u8, (total - cnt),
> +				   CXL_CLEAR_EVENT_MAX_HANDLES);

I might be half asleep but isn't this assuming that (total - cnt)
fits in an u8?  Shouldn't this be min_t(u16, ..) 
Also, maybe u16 cnt would be simpler.

Hmm.  This is safe but only because of how you call it alongside
handling of a particular Get event records response (which must
have fitted in the mailbox and has a longer header).

Looking at this function in isolation, I think the mailbox could be
small enough that we might not fit 255 records + the header.
Perhaps we need a comment to say that, or at minimum a check and error
return if it won't fit?

> +		int i, rc;
> +
> +		for (i = 0; i < nr_recs; i++, cnt++) {
> +			payload.handle[i] = get_pl->records[cnt].hdr.handle;
> +			dev_dbg(cxlds->dev, "Event log '%s': Clearning %u\n",
> +				cxl_event_log_type_str(log),
> +				le16_to_cpu(payload.handle[i]));
> +		}
> +		payload.nr_recs = nr_recs;
> +
> +		rc = cxl_mbox_send_cmd(cxlds, CXL_MBOX_OP_CLEAR_EVENT_RECORD,
> +				       &payload, sizeof(payload), NULL, 0);
> +		if (rc)
> +			return rc;
> +	}
> +
> +	return 0;
> +}
> +
>  static void cxl_mem_get_records_log(struct cxl_dev_state *cxlds,
>  				    enum cxl_event_log_type type)
>  {
> @@ -732,13 +769,22 @@ static void cxl_mem_get_records_log(struct cxl_dev_state *cxlds,
This feels miss named now but I can't immediately think of better naming so on that
basis fine to leave it as is if you don't have a better idea!.

>  		}
>  
>  		nr_rec = le16_to_cpu(payload->record_count);
> -		if (trace_cxl_generic_event_enabled()) {
> +		if (nr_rec > 0) {
>  			int i;
>  
> -			for (i = 0; i < nr_rec; i++)
> -				trace_cxl_generic_event(dev_name(cxlds->dev),
> -							type,
> -							&payload->records[i]);
> +			if (trace_cxl_generic_event_enabled()) {
> +				for (i = 0; i < nr_rec; i++)
> +					trace_cxl_generic_event(dev_name(cxlds->dev),
> +								type,
> +								&payload->records[i]);
> +			}
> +
> +			rc = cxl_clear_event_record(cxlds, type, payload, nr_rec);
> +			if (rc) {
> +				dev_err(cxlds->dev, "Event log '%s': Failed to clear events : %d",
> +					cxl_event_log_type_str(type), rc);
> +				return;
> +			}
>  		}