linux-kernel - Re: [PATCH v1 20/29] cxl/region: Use translated HPA ranges to find the port's decoder

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Message-ID: <Z6Sdos7oc1ZqycR7@rric.localdomain>
Date: Thu, 6 Feb 2025 12:31:46 +0100
From: Robert Richter <rrichter@....com>
To: Gregory Price <gourry@...rry.net>
Cc: 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>,
	Dave Jiang <dave.jiang@...el.com>,
	Davidlohr Bueso <dave@...olabs.net>, linux-cxl@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>,
	Terry Bowman <terry.bowman@....com>
Subject: Re: [PATCH v1 20/29] cxl/region: Use translated HPA ranges to find
 the port's decoder

On 07.01.25 17:33:09, Gregory Price wrote:
> On Tue, Jan 07, 2025 at 03:10:06PM +0100, Robert Richter wrote:
> > This is the second step to find the port's decoder with address
> > translation enabled. The translated HPA range must be used to find a
> > decoder. The port's HPA range is determined by applying address
> > translation when crossing memory domains for the HPA range to each
> > port while traversing the topology from the endpoint up to the port.
> > 
> > Introduce a function cxl_find_auto_decoder() that calculates the
> > port's translated address range to determine the corresponding
> > decoder. Use the existing helper function cxl_port_calc_hpa() for HPA
> > range calculation.
> > 
> > Signed-off-by: Robert Richter <rrichter@....com>
> > ---
> >  drivers/cxl/core/region.c | 63 +++++++++++++++++++++++++++++++++++++--
> >  1 file changed, 61 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> > index 23b86de3d4e7..8d7893878362 100644
> > --- a/drivers/cxl/core/region.c
> > +++ b/drivers/cxl/core/region.c
> > @@ -876,6 +876,66 @@ static int match_auto_decoder(struct device *dev, void *data)
> >  	return 0;
> >  }
> >  
> > +static struct device *
> > +cxl_find_auto_decoder(struct cxl_port *port, struct cxl_endpoint_decoder *cxled,
> > +		      struct cxl_region *cxlr)
> > +{
> > +	struct cxl_port *parent, *iter = cxled_to_port(cxled);
> > +	struct cxl_decoder *cxld = &cxled->cxld;
> > +	struct range hpa = cxld->hpa_range;
> > +	struct cxl_region_ref *rr;
> > +
> > +	while (1) {
> 
> Similar to prior patch, probably we should have while(parent) instead of
> while(1) and be at least a bit defensive against (extremely unlikely) loops.
> 
> At the very least maybe we can express the condition more explicitly.

My review showed there is a bug around the (!parent->to_hpa) check
which is missing the break if (parent == port).

Changed the code using while (iter != port) {} which also fixes this
issue.

-Robert

> 
> > +		parent = parent_port_of(iter);
> > +		if (!parent) {
> > +			dev_warn(&port->dev,
> > +				"port not a parent of endpoint decoder %s\n",
> > +				dev_name(&cxled->cxld.dev));
> > +			return NULL;
> > +		}
> ... snip ...