linux-kernel - Re: [PATCH v8 4/6] cxl/region: Provide region info to the cxl

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Message-ID: <ZA/QSmuc08XFTuUZ@aschofie-mobl2>
Date:   Mon, 13 Mar 2023 18:39:22 -0700
From:   Alison Schofield <alison.schofield@...el.com>
To:     Ira Weiny <ira.weiny@...el.com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 4/6] cxl/region: Provide region info to the cxl_poison
 trace event

On Mon, Mar 13, 2023 at 03:51:31PM -0700, Ira Weiny wrote:
> alison.schofield@ wrote:
> > From: Alison Schofield <alison.schofield@...el.com>
> > 
> > User space may need to know which region, if any, maps the poison
> > address(es) logged in a cxl_poison trace event. Since the mapping
> > of DPAs (device physical addresses) to a region can change, the
> > kernel must provide this information at the time the poison list
> > is read. The event informs user space that at event <timestamp>
> > this <region> mapped to this <DPA>, which is poisoned.
> > 
> > The cxl_poison trace event is already wired up to log the region
> > name and uuid if it receives param 'struct cxl_region'.
> > 
> > In order to provide that cxl_region, add another method for gathering
> > poison - by committed endpoint decoder mappings. This method is only
> > available with CONFIG_CXL_REGION and is only used if a region actually
> > maps the memdev where poison is being read. After the poison list is
> > read for all the mapped resources, poison is read for the unmapped
> > resources, and those events are logged without the region info.
> > 
> > Mixed mode decoders are not currently supported in Linux. Add a debug
> > message to the poison request path. That will serve as an alert that
> > poison list retrieval needs to add support for mixed mode.
> > 
> > The default method remains: read the poison by memdev resource.
> > 
> > Signed-off-by: Alison Schofield <alison.schofield@...el.com>
> 
> [...]
> 
> > diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
> > index ea996057815e..5e65818d2171 100644
> > --- a/drivers/cxl/core/memdev.c
> > +++ b/drivers/cxl/core/memdev.c
> > @@ -139,14 +139,29 @@ static ssize_t trigger_poison_list_store(struct device *dev,
> >  					 const char *buf, size_t len)
> >  {
> >  	struct cxl_memdev *cxlmd = to_cxl_memdev(dev);
> > +	struct cxl_port *port;
> >  	bool trigger;
> >  	int rc;
> >  
> >  	if (kstrtobool(buf, &trigger) || !trigger)
> >  		return -EINVAL;
> >  
> > +	port = dev_get_drvdata(&cxlmd->dev);
> > +	if (!port || !is_cxl_endpoint(port))
> > +		return -EINVAL;
> > +
> >  	down_read(&cxl_dpa_rwsem);
> > -	rc = cxl_get_poison_by_memdev(cxlmd);
> > +	if (port->commit_end == -1) {
> > +		/* No regions mapped to this memdev */
> > +		rc = cxl_get_poison_by_memdev(cxlmd);
> > +	} else {
> > +		/* Regions mapped, collect poison by endpoint */
> > +		rc = device_for_each_child(&port->dev, port,
> > +					   cxl_get_poison_by_endpoint);
> > +		if (rc == 1)
> > +			rc = 0;
> > +	}
> > +
> >  	up_read(&cxl_dpa_rwsem);
> >  
> >  	return rc ? rc : len;
> > diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> > index f29028148806..1a558adfe32d 100644
> > --- a/drivers/cxl/core/region.c
> > +++ b/drivers/cxl/core/region.c
> > @@ -2213,6 +2213,102 @@ struct cxl_pmem_region *to_cxl_pmem_region(struct device *dev)
> >  }
> >  EXPORT_SYMBOL_NS_GPL(to_cxl_pmem_region, CXL);
> >  
> > +int cxl_get_poison_by_endpoint(struct device *dev, void *data)
> > +{
> > +	struct cxl_endpoint_decoder *cxled;
> > +	struct cxl_port *port = data;
> > +	struct cxl_dev_state *cxlds;
> > +	struct cxl_memdev *cxlmd;
> > +	u64 offset, length;
> > +	int rc = 0;
> > +
> > +	down_read(&cxl_dpa_rwsem);
> 
> Oh just realized aren't we already under the read lock when this is called?
> 
> Replacing this with a lockdep_assert() could make the logic here easier.
> 
> Ira

Yes! Thanks for the catch. That will allow removal of the goto out's!


> 
> [...]