cxl/core: Fix potential payload size confusion in cxl_mem_get_poison()

A recent change to cxl_mem_get_records_log() [1] highlighted a subtle
nuance of looping calls to cxl_internal_send_cmd(), i.e. that
cxl_internal_send_cmd() modifies the 'size_out' member of the @mbox_cmd
argument. That mechanism is useful for communicating underflow, but it
is unwanted when reusing @mbox_cmd for a subsequent submission. It turns
out that cxl_xfer_log() avoids this scenario by always redefining
@mbox_cmd each iteration.

Update cxl_mem_get_records_log() and cxl_mem_get_poison() to follow the
same style as cxl_xfer_log(), i.e. re-define @mbox_cmd each iteration.
The cxl_mem_get_records_log() change is just a style fixup, but the
cxl_mem_get_poison() change is a potential fix, per Alison [2]:

    Poison list retrieval can hit this case if the MORE flag is set and
    a follow on read of the list delivers more records than the previous
    read.  ie. device gives one record, sets the _MORE flag, then gives 5.

Not an urgent fix since this behavior has not been seen in the wild,
but worth tracking as a fix.

Cc: Kwangjin Ko <[email protected]>
Cc: Alison Schofield <[email protected]>
Fixes: ed83f7c ("cxl/mbox: Add GET_POISON_LIST mailbox command")
Link: http://lore.kernel.org/r/[email protected] [1]
Link: http://lore.kernel.org/r/ZhAhAL/GOaWFrauw@aschofie-mobl2 [2]
Signed-off-by: Dan Williams <[email protected]>
Reviewed-by: Ira Weiny <[email protected]>
Reviewed-by: Alison Schofield <[email protected]>
Link: https://lore.kernel.org/r/171235441633.2716581.12330082428680958635.stgit@dwillia2-xfh.jf.intel.com
Signed-off-by: Dave Jiang <[email protected]>

Author: djbw

drivers/cxl/core/mbox.c

@@ -946,25 +946,22 @@ static void cxl_mem_get_records_log(struct cxl_memdev_state *mds,
 	struct cxl_memdev *cxlmd = mds->cxlds.cxlmd;
 	struct device *dev = mds->cxlds.dev;
 	struct cxl_get_event_payload *payload;
-	struct cxl_mbox_cmd mbox_cmd;
 	u8 log_type = type;
 	u16 nr_rec;
 
 	mutex_lock(&mds->event.log_lock);
 	payload = mds->event.buf;
 
-	mbox_cmd = (struct cxl_mbox_cmd) {
-		.opcode = CXL_MBOX_OP_GET_EVENT_RECORD,
-		.payload_in = &log_type,
-		.size_in = sizeof(log_type),
-		.payload_out = payload,
-		.min_out = struct_size(payload, records, 0),
-	};
-
 	do {
 		int rc, i;
-
-		mbox_cmd.size_out = mds->payload_size;
+		struct cxl_mbox_cmd mbox_cmd = (struct cxl_mbox_cmd) {
+			.opcode = CXL_MBOX_OP_GET_EVENT_RECORD,
+			.payload_in = &log_type,
+			.size_in = sizeof(log_type),
+			.payload_out = payload,
+			.size_out = mds->payload_size,
+			.min_out = struct_size(payload, records, 0),
+		};
 
 		rc = cxl_internal_send_cmd(mds, &mbox_cmd);
 		if (rc) {
@@ -1297,7 +1294,6 @@ int cxl_mem_get_poison(struct cxl_memdev *cxlmd, u64 offset, u64 len,
 	struct cxl_memdev_state *mds = to_cxl_memdev_state(cxlmd->cxlds);
 	struct cxl_mbox_poison_out *po;
 	struct cxl_mbox_poison_in pi;
-	struct cxl_mbox_cmd mbox_cmd;
 	int nr_records = 0;
 	int rc;
 
@@ -1309,16 +1305,16 @@ int cxl_mem_get_poison(struct cxl_memdev *cxlmd, u64 offset, u64 len,
 	pi.offset = cpu_to_le64(offset);
 	pi.length = cpu_to_le64(len / CXL_POISON_LEN_MULT);
 
-	mbox_cmd = (struct cxl_mbox_cmd) {
-		.opcode = CXL_MBOX_OP_GET_POISON,
-		.size_in = sizeof(pi),
-		.payload_in = &pi,
-		.size_out = mds->payload_size,
-		.payload_out = po,
-		.min_out = struct_size(po, record, 0),
-	};
-
 	do {
+		struct cxl_mbox_cmd mbox_cmd = (struct cxl_mbox_cmd){
+			.opcode = CXL_MBOX_OP_GET_POISON,
+			.size_in = sizeof(pi),
+			.payload_in = &pi,
+			.size_out = mds->payload_size,
+			.payload_out = po,
+			.min_out = struct_size(po, record, 0),
+		};
+
 		rc = cxl_internal_send_cmd(mds, &mbox_cmd);
 		if (rc)
 			break;