diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
index 90664659d5fa..3600b7cbfb58 100644
--- a/drivers/cxl/core/hdm.c
+++ b/drivers/cxl/core/hdm.c
@@ -52,6 +52,14 @@ int devm_cxl_add_passthrough_decoder(struct cxl_port *port)
 	struct cxl_dport *dport = NULL;
 	int single_port_map[1];
 	unsigned long index;
+	struct cxl_hdm *cxlhdm = dev_get_drvdata(&port->dev);
+
+	/*
+	 * Capability checks are moot for passthrough decoders, support
+	 * any and all possibilities.
+	 */
+	cxlhdm->interleave_mask = ~0U;
+	cxlhdm->iw_cap_mask = ~0UL;
 
 	cxlsd = cxl_switch_decoder_alloc(port, 1);
 	if (IS_ERR(cxlsd))
@@ -79,6 +87,11 @@ static void parse_hdm_decoder_caps(struct cxl_hdm *cxlhdm)
 		cxlhdm->interleave_mask |= GENMASK(11, 8);
 	if (FIELD_GET(CXL_HDM_DECODER_INTERLEAVE_14_12, hdm_cap))
 		cxlhdm->interleave_mask |= GENMASK(14, 12);
+	cxlhdm->iw_cap_mask = BIT(1) | BIT(2) | BIT(4) | BIT(8);
+	if (FIELD_GET(CXL_HDM_DECODER_INTERLEAVE_3_6_12_WAY, hdm_cap))
+		cxlhdm->iw_cap_mask |= BIT(3) | BIT(6) | BIT(12);
+	if (FIELD_GET(CXL_HDM_DECODER_INTERLEAVE_16_WAY, hdm_cap))
+		cxlhdm->iw_cap_mask |= BIT(16);
 }
 
 static int map_hdm_decoder_regs(struct cxl_port *port, void __iomem *crb,
diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index 0d59af19ecee..bc5a43897d57 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -997,6 +997,26 @@ static int cxl_port_attach_region(struct cxl_port *port,
 	}
 	cxld = cxl_rr->decoder;
 
+	/*
+	 * the number of targets should not exceed the target_count
+	 * of the decoder
+	 */
+	if (is_switch_decoder(&cxld->dev)) {
+		struct cxl_switch_decoder *cxlsd;
+
+		cxlsd = to_cxl_switch_decoder(&cxld->dev);
+		if (cxl_rr->nr_targets > cxlsd->nr_targets) {
+			dev_dbg(&cxlr->dev,
+				"%s:%s %s add: %s:%s @ %d overflows targets: %d\n",
+				dev_name(port->uport_dev), dev_name(&port->dev),
+				dev_name(&cxld->dev), dev_name(&cxlmd->dev),
+				dev_name(&cxled->cxld.dev), pos,
+				cxlsd->nr_targets);
+			rc = -ENXIO;
+			goto out_erase;
+		}
+	}
+
 	rc = cxl_rr_ep_add(cxl_rr, cxled);
 	if (rc) {
 		dev_dbg(&cxlr->dev,
@@ -1106,6 +1126,50 @@ static int check_last_peer(struct cxl_endpoint_decoder *cxled,
 	return 0;
 }
 
+static int check_interleave_cap(struct cxl_decoder *cxld, int iw, int ig)
+{
+	struct cxl_port *port = to_cxl_port(cxld->dev.parent);
+	struct cxl_hdm *cxlhdm = dev_get_drvdata(&port->dev);
+	unsigned int interleave_mask;
+	u8 eiw;
+	u16 eig;
+	int high_pos, low_pos;
+
+	if (!test_bit(iw, &cxlhdm->iw_cap_mask))
+		return -ENXIO;
+	/*
+	 * Per CXL specification r3.1(8.2.4.20.13 Decoder Protection),
+	 * if eiw < 8:
+	 *   DPAOFFSET[51: eig + 8] = HPAOFFSET[51: eig + 8 + eiw]
+	 *   DPAOFFSET[eig + 7: 0]  = HPAOFFSET[eig + 7: 0]
+	 *
+	 *   when the eiw is 0, all the bits of HPAOFFSET[51: 0] are used, the
+	 *   interleave bits are none.
+	 *
+	 * if eiw >= 8:
+	 *   DPAOFFSET[51: eig + 8] = HPAOFFSET[51: eig + eiw] / 3
+	 *   DPAOFFSET[eig + 7: 0]  = HPAOFFSET[eig + 7: 0]
+	 *
+	 *   when the eiw is 8, all the bits of HPAOFFSET[51: 0] are used, the
+	 *   interleave bits are none.
+	 */
+	ways_to_eiw(iw, &eiw);
+	if (eiw == 0 || eiw == 8)
+		return 0;
+
+	granularity_to_eig(ig, &eig);
+	if (eiw > 8)
+		high_pos = eiw + eig - 1;
+	else
+		high_pos = eiw + eig + 7;
+	low_pos = eig + 8;
+	interleave_mask = GENMASK(high_pos, low_pos);
+	if (interleave_mask & ~cxlhdm->interleave_mask)
+		return -ENXIO;
+
+	return 0;
+}
+
 static int cxl_port_setup_targets(struct cxl_port *port,
 				  struct cxl_region *cxlr,
 				  struct cxl_endpoint_decoder *cxled)
@@ -1256,6 +1320,15 @@ static int cxl_port_setup_targets(struct cxl_port *port,
 			return -ENXIO;
 		}
 	} else {
+		rc = check_interleave_cap(cxld, iw, ig);
+		if (rc) {
+			dev_dbg(&cxlr->dev,
+				"%s:%s iw: %d ig: %d is not supported\n",
+				dev_name(port->uport_dev),
+				dev_name(&port->dev), iw, ig);
+			return rc;
+		}
+
 		cxld->interleave_ways = iw;
 		cxld->interleave_granularity = ig;
 		cxld->hpa_range = (struct range) {
@@ -1692,6 +1765,15 @@ static int cxl_region_attach(struct cxl_region *cxlr,
 	struct cxl_dport *dport;
 	int rc = -ENXIO;
 
+	rc = check_interleave_cap(&cxled->cxld, p->interleave_ways,
+				  p->interleave_granularity);
+	if (rc) {
+		dev_dbg(&cxlr->dev, "%s iw: %d ig: %d is not supported\n",
+			dev_name(&cxled->cxld.dev), p->interleave_ways,
+			p->interleave_granularity);
+		return rc;
+	}
+
 	if (cxled->mode != cxlr->mode) {
 		dev_dbg(&cxlr->dev, "%s region mode: %d mismatch: %d\n",
 			dev_name(&cxled->cxld.dev), cxlr->mode, cxled->mode);
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index de2c250c894b..bb3ad219b6b3 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -43,6 +43,8 @@
 #define   CXL_HDM_DECODER_TARGET_COUNT_MASK GENMASK(7, 4)
 #define   CXL_HDM_DECODER_INTERLEAVE_11_8 BIT(8)
 #define   CXL_HDM_DECODER_INTERLEAVE_14_12 BIT(9)
+#define   CXL_HDM_DECODER_INTERLEAVE_3_6_12_WAY BIT(11)
+#define   CXL_HDM_DECODER_INTERLEAVE_16_WAY BIT(12)
 #define CXL_HDM_DECODER_CTRL_OFFSET 0x4
 #define   CXL_HDM_DECODER_ENABLE BIT(1)
 #define CXL_HDM_DECODER0_BASE_LOW_OFFSET(i) (0x20 * (i) + 0x10)
diff --git a/drivers/cxl/cxlmem.h b/drivers/cxl/cxlmem.h
index 6933bc20e76b..59c7f88b915a 100644
--- a/drivers/cxl/cxlmem.h
+++ b/drivers/cxl/cxlmem.h
@@ -888,11 +888,21 @@ static inline void cxl_mem_active_dec(void)
 
 int cxl_mem_sanitize(struct cxl_memdev *cxlmd, u16 cmd);
 
+/**
+ * struct cxl_hdm - HDM Decoder registers and cached / decoded capabilities
+ * @regs: mapped registers, see devm_cxl_setup_hdm()
+ * @decoder_count: number of decoders for this port
+ * @target_count: for switch decoders, max downstream port targets
+ * @interleave_mask: interleave granularity capability, see check_interleave_cap()
+ * @iw_cap_mask: bitmask of supported interleave ways, see check_interleave_cap()
+ * @port: mapped cxl_port, see devm_cxl_setup_hdm()
+ */
 struct cxl_hdm {
 	struct cxl_component_regs regs;
 	unsigned int decoder_count;
 	unsigned int target_count;
 	unsigned int interleave_mask;
+	unsigned long iw_cap_mask;
 	struct cxl_port *port;
 };
 
diff --git a/tools/testing/cxl/test/cxl.c b/tools/testing/cxl/test/cxl.c
index f4e517a0c774..8251718eaf3a 100644
--- a/tools/testing/cxl/test/cxl.c
+++ b/tools/testing/cxl/test/cxl.c
@@ -624,11 +624,15 @@ static struct cxl_hdm *mock_cxl_setup_hdm(struct cxl_port *port,
 					  struct cxl_endpoint_dvsec_info *info)
 {
 	struct cxl_hdm *cxlhdm = devm_kzalloc(&port->dev, sizeof(*cxlhdm), GFP_KERNEL);
+	struct device *dev = &port->dev;
 
 	if (!cxlhdm)
 		return ERR_PTR(-ENOMEM);
 
 	cxlhdm->port = port;
+	cxlhdm->interleave_mask = ~0U;
+	cxlhdm->iw_cap_mask = ~0UL;
+	dev_set_drvdata(dev, cxlhdm);
 	return cxlhdm;
 }