Re: [PATCH v4 1/4] cxl/hdm: Reject switch decoder interleave ways that overflow targets

On Wed, Jul 22, 2026 at 01:55:47AM +0100, Jonathan Cameron wrote:
> On Mon, 20 Jul 2026 18:59:37 -0700
> Alison Schofield <[email protected]> wrote:
> 
> > Switch decoder enumeration validates that the interleave ways encoding
> > is legal, but not that the resulting number of ways fits the available
> > targets. This can overrun the target arrays during enumeration.
> > 
> > Reject committed decoders whose interleave ways exceed either the
> > hardware target list capacity or the reported target count. Reject
> > switch decoders that report zero targets.
> > 
> > For uncommitted decoders, ignore the stale interleave ways value and
> > reset it to one until the decoder is committed.
> > 
> > Add a clarifying comment that target_count is a direct count, not
> > 0-based like decoder_count.
> > 
> > Link: https://sashiko.dev/#/patchset/[email protected]?part=1
> > Fixes: d17d0540a0db ("cxl/core/hdm: Add CXL standard decoder enumeration to the core")
> > Signed-off-by: Alison Schofield <[email protected]>
> 
> oops. I replied to v3 after you sent this out. Please take a look.

Reply for patch one is back on v3. It all was still relevant for v4.

> 
> Thanks,
> 
> Jonathan
> 
> > ---
> >  drivers/cxl/core/hdm.c | 33 +++++++++++++++++++++++++++++++++
> >  drivers/cxl/cxl.h      |  2 ++
> >  2 files changed, 35 insertions(+)
> > 
> > diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> > index 0c80b76a5f9b..d81df45d8005 100644
> > --- a/drivers/cxl/core/hdm.c
> > +++ b/drivers/cxl/core/hdm.c
> > @@ -76,6 +76,8 @@ static void parse_hdm_decoder_caps(struct cxl_hdm *cxlhdm)
> >  
> >  	hdm_cap = readl(cxlhdm->regs.hdm_decoder + CXL_HDM_DECODER_CAP_OFFSET);
> >  	cxlhdm->decoder_count = cxl_hdm_decoder_count(hdm_cap);
> > +
> > +	/* target_count is a direct count (1h..8h), not 0-based like decoder_count */
> >  	cxlhdm->target_count =
> >  		FIELD_GET(CXL_HDM_DECODER_TARGET_COUNT_MASK, hdm_cap);
> >  	if (FIELD_GET(CXL_HDM_DECODER_INTERLEAVE_11_8, hdm_cap))
> > @@ -1084,6 +1086,37 @@ static int init_hdm_decoder(struct cxl_port *port, struct cxl_decoder *cxld,
> >  		cxld->interleave_ways, cxld->interleave_granularity);
> >  
> >  	if (!cxled) {
> > +		struct cxl_switch_decoder *cxlsd =
> > +			to_cxl_switch_decoder(&cxld->dev);
> > +
> > +		if (cxlsd->nr_targets < 1) {
> > +			dev_err(&port->dev,
> > +				"decoder%d.%d: reports zero targets\n",
> > +				port->id, cxld->id);
> > +			return -ENXIO;
> > +		}
> > +
> > +		if (!committed) {
> > +			/* Ignore interleave ways until commit */
> > +			cxld->interleave_ways = 1;
> > +			return 0;
> > +		}
> > +
> > +		if (cxld->interleave_ways > CXL_HDM_DECODER0_TL_TARGETS) {
> > +			dev_err(&port->dev,
> > +				"decoder%d.%d: interleave ways: %d exceeds target list capacity: %d\n",
> > +				port->id, cxld->id, cxld->interleave_ways,
> > +				CXL_HDM_DECODER0_TL_TARGETS);
> > +			return -ENXIO;
> > +		}
> > +		if (cxld->interleave_ways > cxlsd->nr_targets) {
> > +			dev_err(&port->dev,
> > +				"decoder%d.%d: interleave ways: %d exceeds targets: %d\n",
> > +				port->id, cxld->id, cxld->interleave_ways,
> > +				cxlsd->nr_targets);
> > +			return -ENXIO;
> > +		}
> > +
> >  		lo = readl(hdm + CXL_HDM_DECODER0_TL_LOW(which));
> >  		hi = readl(hdm + CXL_HDM_DECODER0_TL_HIGH(which));
> >  		target_list.value = (hi << 32) + lo;
> > diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> > index c0e5308e4d1b..291ada46b646 100644
> > --- a/drivers/cxl/cxl.h
> > +++ b/drivers/cxl/cxl.h
> > @@ -67,6 +67,8 @@ extern const struct nvdimm_security_ops *cxl_security_ops;
> >  #define   CXL_HDM_DECODER0_CTRL_HOSTONLY BIT(12)
> >  #define CXL_HDM_DECODER0_TL_LOW(i) (0x20 * (i) + 0x24)
> >  #define CXL_HDM_DECODER0_TL_HIGH(i) (0x20 * (i) + 0x28)
> > +/* Two registers with one target ID per byte */
> > +#define CXL_HDM_DECODER0_TL_TARGETS 8
> >  #define CXL_HDM_DECODER0_SKIP_LOW(i) CXL_HDM_DECODER0_TL_LOW(i)
> >  #define CXL_HDM_DECODER0_SKIP_HIGH(i) CXL_HDM_DECODER0_TL_HIGH(i)
> >  
>