[PATCH -qemu 0/2] hw/cxl: Media Operation Discovery fixles

[PATCH -qemu 0/2] hw/cxl: Media Operation Discovery fixles

[Davidlohr Bueso]

Hello,

While working on the driver side of this, I tripped on two qemu issues
around discovery semantics. I think this is the first time these code
paths are exercised.

Applies against 'cxl-2026-01-09-draft'.

Thanks!

Davidlohr Bueso (2):
  hw/cxl: Respect Media Operation max ops discovery semantics
  hw/cxl: Exclude Discovery from Media Operation Discovery output

 hw/cxl/cxl-mailbox-utils.c | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

-- 
2.39.5

[PATCH 1/2] hw/cxl: Respect Media Operation max ops discovery semantics

[Davidlohr Bueso]

The Discovery handler rejects requests where start_index + num_ops
exceeds the total number of supported operations. Per CXL 4.0
Table 8-332, num_ops is the "Maximum number of Media Operation to
return" - a maximum, not an exact count. The device should return
up to that many entries, not reject the request.

Cap num_ops to the available entries from start_index instead of
erroring the command.

Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
---
 hw/cxl/cxl-mailbox-utils.c | 25 +++++++++++--------------
 1 file changed, 11 insertions(+), 14 deletions(-)

diff --git a/hw/cxl/cxl-mailbox-utils.c b/hw/cxl/cxl-mailbox-utils.c
index a3143f3faa23..71a012121c87 100644
--- a/hw/cxl/cxl-mailbox-utils.c
+++ b/hw/cxl/cxl-mailbox-utils.c
@@ -2593,6 +2593,7 @@ static CXLRetCode media_operations_discovery(uint8_t *payload_in,
     } QEMU_PACKED *media_op_in_disc_pl = (void *)payload_in;
     struct media_op_discovery_out_pl *media_out_pl =
         (struct media_op_discovery_out_pl *)payload_out;
+    int total = ARRAY_SIZE(media_op_matrix);
     int num_ops, start_index, i;
     int count = 0;
 
@@ -2609,24 +2610,20 @@ static CXLRetCode media_operations_discovery(uint8_t *payload_in,
      * sub class command.
      */
     if (media_op_in_disc_pl->dpa_range_count ||
-        start_index + num_ops > ARRAY_SIZE(media_op_matrix)) {
+        start_index >= total) {
         return CXL_MBOX_INVALID_INPUT;
     }
 
     media_out_pl->dpa_range_granularity = CXL_CACHE_LINE_SIZE;
-    media_out_pl->total_supported_operations =
-                                     ARRAY_SIZE(media_op_matrix);
-    if (num_ops > 0) {
-        for (i = start_index; i < start_index + num_ops; i++) {
-            media_out_pl->entry[count].media_op_class =
-                    media_op_matrix[i].media_op_class;
-            media_out_pl->entry[count].media_op_subclass =
-                        media_op_matrix[i].media_op_subclass;
-            count++;
-            if (count == num_ops) {
-                break;
-            }
-        }
+    media_out_pl->total_supported_operations = total;
+
+    num_ops = MIN(num_ops, total - start_index);
+    for (i = 0; i < num_ops; i++) {
+        media_out_pl->entry[count].media_op_class =
+                media_op_matrix[start_index + i].media_op_class;
+        media_out_pl->entry[count].media_op_subclass =
+                    media_op_matrix[start_index + i].media_op_subclass;
+        count++;
     }
 
     media_out_pl->num_of_supported_operations = count;
-- 
2.39.5

[PATCH 2/2] hw/cxl: Exclude Discovery from Media Operation Discovery output

[Davidlohr Bueso]

Per CXL 4.0 Table 8-331, the Discovery operation "returns a list of
all Media Operations that the device supports, with the exception of
the Discovery operation (Class=0, Subclass=0)."

Filter out Discovery entries when building the output list and adjust
total_supported_operations accordingly.

Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
---
 hw/cxl/cxl-mailbox-utils.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/hw/cxl/cxl-mailbox-utils.c b/hw/cxl/cxl-mailbox-utils.c
index 71a012121c87..90540f59dedd 100644
--- a/hw/cxl/cxl-mailbox-utils.c
+++ b/hw/cxl/cxl-mailbox-utils.c
@@ -2593,7 +2593,10 @@ static CXLRetCode media_operations_discovery(uint8_t *payload_in,
     } QEMU_PACKED *media_op_in_disc_pl = (void *)payload_in;
     struct media_op_discovery_out_pl *media_out_pl =
         (struct media_op_discovery_out_pl *)payload_out;
-    int total = ARRAY_SIZE(media_op_matrix);
+    /*
+     * Per Table 8-331, the returned list excludes Discovery (entry 0).
+     */
+    int total = ARRAY_SIZE(media_op_matrix) - 1;
     int num_ops, start_index, i;
     int count = 0;
 
@@ -2619,10 +2622,12 @@ static CXLRetCode media_operations_discovery(uint8_t *payload_in,
 
     num_ops = MIN(num_ops, total - start_index);
     for (i = 0; i < num_ops; i++) {
+        int idx = start_index + i + 1; /* +1 skips Discovery at entry 0 */
+
         media_out_pl->entry[count].media_op_class =
-                media_op_matrix[start_index + i].media_op_class;
+                media_op_matrix[idx].media_op_class;
         media_out_pl->entry[count].media_op_subclass =
-                    media_op_matrix[start_index + i].media_op_subclass;
+                    media_op_matrix[idx].media_op_subclass;
         count++;
     }
 
-- 
2.39.5