[PATCH v4 25/28] cxl/region: Read existing extents on region creation

[ira . weiny]

From: Navneet Singh <navneet.singh@xxxxxxxxx>

Dynamic capacity device extents may be left in an accepted state on a
device due to an unexpected host crash.  In this case it is expected
that the creation of a new region on top of a DC partition can read
those extents and surface them for continued use.

Once all endpoint decoders are part of a region and the region is being
realized, a read of the 'devices extent list' can reveal these
previously accepted extents.

CXL r3.1 specifies the mailbox call Get Dynamic Capacity Extent List for
this purpose.  The call returns all the extents for all dynamic capacity
partitions.  If the fabric manager is adding extents to any DCD
partition, the extent list for the recovered region may change.  In this
case the query must retry.  Upon retry the query could encounter extents
which were accepted on a previous list query.  Adding such extents is
ignored without error because they are entirely within a previous
accepted extent.

The scan for existing extents races with the dax_cxl driver.  This is
synchronized through the region device lock.  Extents which are found
after the driver has loaded will surface through the normal notification
path while extents seen prior to the driver are read during driver load.

Signed-off-by: Navneet Singh <navneet.singh@xxxxxxxxx>
Co-developed-by: Ira Weiny <ira.weiny@xxxxxxxxx>
Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>

---
Changes:
[iweiny: adjust for mailbox split]

[djiang: Update commit messages]
[djiang: s/cxl_read_extent_list/cxl_process_extent_list/]
[djiang: #define CXL_READ_EXTENT_LIST_RETRY]
---
 drivers/cxl/core/core.h   |   2 +
 drivers/cxl/core/mbox.c   | 105 ++++++++++++++++++++++++++++++++++++++++++++++
 drivers/cxl/core/region.c |  12 ++++++
 drivers/cxl/cxlmem.h      |  21 ++++++++++
 4 files changed, 140 insertions(+)

diff --git a/drivers/cxl/core/core.h b/drivers/cxl/core/core.h
index 0eccdd0b9261..80d61f75161d 100644
--- a/drivers/cxl/core/core.h
+++ b/drivers/cxl/core/core.h
@@ -21,6 +21,8 @@ cxled_to_mds(struct cxl_endpoint_decoder *cxled)
 	return container_of(cxlds, struct cxl_memdev_state, cxlds);
 }
 
+void cxl_process_extent_list(struct cxl_endpoint_decoder *cxled);
+
 #ifdef CONFIG_CXL_REGION
 extern struct device_attribute dev_attr_create_pmem_region;
 extern struct device_attribute dev_attr_create_ram_region;
diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
index d66beec687a0..6b25d15403a3 100644
--- a/drivers/cxl/core/mbox.c
+++ b/drivers/cxl/core/mbox.c
@@ -1697,6 +1697,111 @@ int cxl_dev_dynamic_capacity_identify(struct cxl_memdev_state *mds)
 }
 EXPORT_SYMBOL_NS_GPL(cxl_dev_dynamic_capacity_identify, CXL);
 
+/* Return -EAGAIN if the extent list changes while reading */
+static int __cxl_process_extent_list(struct cxl_endpoint_decoder *cxled)
+{
+	u32 current_index, total_read, total_expected, initial_gen_num;
+	struct cxl_memdev_state *mds = cxled_to_mds(cxled);
+	struct cxl_mailbox *cxl_mbox = &mds->cxlds.cxl_mbox;
+	struct device *dev = mds->cxlds.dev;
+	struct cxl_mbox_cmd mbox_cmd;
+	u32 max_extent_count;
+	bool first = true;
+
+	struct cxl_mbox_get_extent_out *extents __free(kfree) =
+				kvmalloc(cxl_mbox->payload_size, GFP_KERNEL);
+	if (!extents)
+		return -ENOMEM;
+
+	total_read = 0;
+	current_index = 0;
+	total_expected = 0;
+	max_extent_count = (cxl_mbox->payload_size - sizeof(*extents)) /
+				sizeof(struct cxl_extent);
+	do {
+		struct cxl_mbox_get_extent_in get_extent;
+		u32 nr_returned, current_total, current_gen_num;
+		int rc;
+
+		get_extent = (struct cxl_mbox_get_extent_in) {
+			.extent_cnt = max(max_extent_count,
+					  total_expected - current_index),
+			.start_extent_index = cpu_to_le32(current_index),
+		};
+
+		mbox_cmd = (struct cxl_mbox_cmd) {
+			.opcode = CXL_MBOX_OP_GET_DC_EXTENT_LIST,
+			.payload_in = &get_extent,
+			.size_in = sizeof(get_extent),
+			.size_out = cxl_mbox->payload_size,
+			.payload_out = extents,
+			.min_out = 1,
+		};
+
+		rc = cxl_internal_send_cmd(cxl_mbox, &mbox_cmd);
+		if (rc < 0)
+			return rc;
+
+		/* Save initial data */
+		if (first) {
+			total_expected = le32_to_cpu(extents->total_extent_count);
+			initial_gen_num = le32_to_cpu(extents->generation_num);
+			first = false;
+		}
+
+		nr_returned = le32_to_cpu(extents->returned_extent_count);
+		total_read += nr_returned;
+		current_total = le32_to_cpu(extents->total_extent_count);
+		current_gen_num = le32_to_cpu(extents->generation_num);
+
+		dev_dbg(dev, "Got extent list %d-%d of %d generation Num:%d\n",
+			current_index, total_read - 1, current_total, current_gen_num);
+
+		if (current_gen_num != initial_gen_num || total_expected != current_total) {
+			dev_dbg(dev, "Extent list change detected; gen %u != %u : cnt %u != %u\n",
+				current_gen_num, initial_gen_num,
+				total_expected, current_total);
+			return -EAGAIN;
+		}
+
+		for (int i = 0; i < nr_returned ; i++) {
+			struct cxl_extent *extent = &extents->extent[i];
+
+			dev_dbg(dev, "Processing extent %d/%d\n",
+				current_index + i, total_expected);
+
+			rc = validate_add_extent(mds, extent);
+			if (rc)
+				continue;
+		}
+
+		current_index += nr_returned;
+	} while (total_expected > total_read);
+
+	return 0;
+}
+
+/**
+ * cxl_process_extent_list() - Read existing extents
+ * @cxled: Endpoint decoder which is part of a region
+ *
+ * Issue the Get Dynamic Capacity Extent List command to the device
+ * and add existing extents if found.
+ *
+ * A retry of 10 is somewhat arbitrary, however, extent changes should be
+ * relatively rare while bringing up a region.  So 10 should be plenty.
+ */
+#define CXL_READ_EXTENT_LIST_RETRY 10
+void cxl_process_extent_list(struct cxl_endpoint_decoder *cxled)
+{
+	int retry = CXL_READ_EXTENT_LIST_RETRY;
+	int rc;
+
+	do {
+		rc = __cxl_process_extent_list(cxled);
+	} while (rc == -EAGAIN && retry--);
+}
+
 static int add_dpa_res(struct device *dev, struct resource *parent,
 		       struct resource *res, resource_size_t start,
 		       resource_size_t size, const char *type)
diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index 6ae51fc2bdae..5ed4a77491e5 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -3190,6 +3190,15 @@ static int devm_cxl_add_pmem_region(struct cxl_region *cxlr)
 	return rc;
 }
 
+static void cxlr_add_existing_extents(struct cxl_region *cxlr)
+{
+	struct cxl_region_params *p = &cxlr->params;
+	int i;
+
+	for (i = 0; i < p->nr_targets; i++)
+		cxl_process_extent_list(p->targets[i]);
+}
+
 static void cxlr_dax_unregister(void *_cxlr_dax)
 {
 	struct cxl_dax_region *cxlr_dax = _cxlr_dax;
@@ -3224,6 +3233,9 @@ static int devm_cxl_add_dax_region(struct cxl_region *cxlr)
 	dev_dbg(&cxlr->dev, "%s: register %s\n", dev_name(dev->parent),
 		dev_name(dev));
 
+	if (cxlr->mode == CXL_REGION_DC)
+		cxlr_add_existing_extents(cxlr);
+
 	return devm_add_action_or_reset(&cxlr->dev, cxlr_dax_unregister,
 					cxlr_dax);
 err:
diff --git a/drivers/cxl/cxlmem.h b/drivers/cxl/cxlmem.h
index dd7cc0d373af..4272f134da8f 100644
--- a/drivers/cxl/cxlmem.h
+++ b/drivers/cxl/cxlmem.h
@@ -626,6 +626,27 @@ struct cxl_mbox_dc_response {
 	} __packed extent_list[];
 } __packed;
 
+/*
+ * Get Dynamic Capacity Extent List; Input Payload
+ * CXL rev 3.1 section 8.2.9.9.9.2; Table 8-166
+ */
+struct cxl_mbox_get_extent_in {
+	__le32 extent_cnt;
+	__le32 start_extent_index;
+} __packed;
+
+/*
+ * Get Dynamic Capacity Extent List; Output Payload
+ * CXL rev 3.1 section 8.2.9.9.9.2; Table 8-167
+ */
+struct cxl_mbox_get_extent_out {
+	__le32 returned_extent_count;
+	__le32 total_extent_count;
+	__le32 generation_num;
+	u8 rsvd[4];
+	struct cxl_extent extent[];
+} __packed;
+
 struct cxl_mbox_get_supported_logs {
 	__le16 entries;
 	u8 rsvd[6];

-- 
2.46.0