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Date:   Thu, 1 Dec 2022 07:30:30 -0800
From:   Ira Weiny <ira.weiny@intel.com>
To:     Jonathan Cameron <Jonathan.Cameron@huawei.com>
CC:     Dan Williams <dan.j.williams@intel.com>,
        Alison Schofield <alison.schofield@intel.com>,
        Vishal Verma <vishal.l.verma@intel.com>,
        "Ben Widawsky" <bwidawsk@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Dave Jiang <dave.jiang@intel.com>,
        <linux-kernel@vger.kernel.org>, <linux-cxl@vger.kernel.org>
Subject: Re: [PATCH V2 03/11] cxl/mem: Implement Clear Event Records command
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References: <20221201002719.2596558-1-ira.weiny@intel.com>
 <20221201002719.2596558-4-ira.weiny@intel.com>
 <20221201132618.00006602@Huawei.com>
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On Thu, Dec 01, 2022 at 01:26:18PM +0000, Jonathan Cameron wrote:
> On Wed, 30 Nov 2022 16:27:11 -0800
> ira.weiny@intel.com wrote:
> 
> > From: Ira Weiny <ira.weiny@intel.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@intel.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@huawei.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, ..) 

This cast will ensure the value is never out of range for nr_recs which needs
to be u8 and (total - cnt) will never be negative.

But now you have me double thinking myself.

> 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?

I did not realize that Payload Size applied to input payloads as well.  :-/
There is no check in the send command for that ATM.  Looking at the spec I
think you are right.

I'll further limit the payload size here too.

And with this I might get rid of the min_t() and just cap based on that value.

> 
> > +		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!.

So we leave it.  Naming is hard!  :-D

Thanks for the quick review, V3 coming ASAP.
Ira