Re: [PATCH v2 1/3] cxl/hdm: Reject switch decoder interleave ways that overflow targets

[Richard Cheng <icheng@nvidia.com>]

On Wed, Jul 15, 2026 at 02:45:47PM +0800, Alison Schofield 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/20260711180755.1779002-1-alison.schofield@intel.com?part=1
> Fixes: d17d0540a0db ("cxl/core/hdm: Add CXL standard decoder enumeration to the core")
> Signed-off-by: Alison Schofield <alison.schofield@intel.com>
> ---
>  drivers/cxl/core/hdm.c  | 26 ++++++++++++++++++++++++++
>  drivers/cxl/core/port.c |  2 +-
>  drivers/cxl/cxl.h       |  2 ++
>  3 files changed, 29 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> index 0c80b76a5f9b..9f005f3193e2 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 +1086,30 @@ 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 (!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/core/port.c b/drivers/cxl/core/port.c
> index 1215ee4f4035..28eccfdd75b8 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c
> @@ -1979,7 +1979,7 @@ static int cxl_switch_decoder_init(struct cxl_port *port,
>  				   struct cxl_switch_decoder *cxlsd,
>  				   int nr_targets)
>  {
> -	if (nr_targets > CXL_DECODER_MAX_INTERLEAVE)
> +	if (nr_targets < 1 || nr_targets > CXL_DECODER_MAX_INTERLEAVE)

This contradict to what the comment claims.
The comment says that Target Count is a direct cound with 1h to 8h. However,
this check uses CXL_DECODER_MAX_INTERLEAVE, which is 16.

I think since the capability field is 4 bits wide, values 9 to 15 are still
acceptable.

I'm confused by this part, it looks inconsistent, refusing enumeration above 9
doesn't make sense to me either.
Maybe some explanation to explain why ?

Best regards,
Richard Cheng.
>  		return -EINVAL;
>  
>  	cxlsd->nr_targets = nr_targets;
> 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)
>  
> -- 
> 2.37.3
> 
>