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

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]>
---
 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)
 
-- 
2.37.3