On Thu, 27 Feb 2025 22:38:15 +0000 <shiju.jose@xxxxxxxxxx> wrote: > From: Shiju Jose <shiju.jose@xxxxxxxxxx> > > Memory sparing is defined as a repair function that replaces a portion of > memory with a portion of functional memory at that same DPA. The subclasses > for this operation vary in terms of the scope of the sparing being > performed. The cacheline sparing subclass refers to a sparing action that > can replace a full cacheline. Row sparing is provided as an alternative to > PPR sparing functions and its scope is that of a single DDR row. > As per CXL r3.2 Table 8-125 foot note 1. Memory sparing is preferred over > PPR when possible. > Bank sparing allows an entire bank to be replaced. Rank sparing is defined > as an operation in which an entire DDR rank is replaced. > > Memory sparing maintenance operations may be supported by CXL devices > that implement CXL.mem protocol. A sparing maintenance operation requests > the CXL device to perform a repair operation on its media. > For example, a CXL device with DRAM components that support memory sparing > features may implement sparing maintenance operations. > > The host may issue a query command by setting query resources flag in the > input payload (CXL spec 3.2 Table 8-120) to determine availability of > sparing resources for a given address. In response to a query request, > the device shall report the resource availability by producing the memory > sparing event record (CXL spec 3.2 Table 8-60) in which the Channel, Rank, > Nibble Mask, Bank Group, Bank, Row, Column, Sub-Channel fields are a copy > of the values specified in the request. > > During the execution of a sparing maintenance operation, a CXL memory > device: > - may not retain data > - may not be able to process CXL.mem requests correctly. > These CXL memory device capabilities are specified by restriction flags > in the memory sparing feature readable attributes. > > When a CXL device identifies error on a memory component, the device > may inform the host about the need for a memory sparing maintenance > operation by using DRAM event record, where the 'maintenance needed' flag > may set. The event record contains some of the DPA, Channel, Rank, > Nibble Mask, Bank Group, Bank, Row, Column, Sub-Channel fields that > should be repaired. The userspace tool requests for maintenance operation > if the 'maintenance needed' flag set in the CXL DRAM error record. > > CXL spec 3.2 section 8.2.10.7.1.4 describes the device's memory sparing > maintenance operation feature. > > CXL spec 3.2 section 8.2.10.7.2.3 describes the memory sparing feature > discovery and configuration. > > Add support for controlling CXL memory device memory sparing feature. > Register with EDAC driver, which gets the memory repair attr descriptors > from the EDAC memory repair driver and exposes sysfs repair control > attributes for memory sparing to the userspace. For example CXL memory > sparing control for the CXL mem0 device is exposed in > /sys/bus/edac/devices/cxl_mem0/mem_repairX/ > > Use case > ======== > 1. CXL device identifies a failure in a memory component, report to > userspace in a CXL DRAM trace event with DPA and other attributes of > memory to repair such as channel, rank, nibble mask, bank Group, > bank, row, column, sub-channel. > > 2. Rasdaemon process the trace event and may issue query request in sysfs > check resources available for memory sparing if either of the following > conditions met. > - 'maintenance needed' flag set in the event record. > - 'threshold event' flag set for CVME threshold feature. > - If the previous case is not enough, may be when the number of corrected > error reported on a CXL.mem media to the user space exceeds an error > threshold set in the userspace policy. > > 3. Rasdaemon process the memory sparing trace event and issue repair > request for memory sparing. > > Kernel CXL driver shall report memory sparing event record to the userspace > with the resource availability in order rasdaemon to process the event > record and issue a repair request in sysfs for the memory sparing operation > in the CXL device. > > Note: Based on the feedbacks from the community 'query' sysfs attribute is > removed and reporting memory sparing error record to the userspace are not > supported. Instead userspace issues sparing operation and kernel does the > same to the CXL memory device, when 'maintenance needed' flag set in the > DRAM event record. > > Add checks to ensure the memory to be repaired is offline and if online, > then originates from a CXL DRAM error record reported in the current boot > before requesting a memory sparing operation on the device. > > Tested for memory sparing control feature with > "hw/cxl: Add memory sparing control feature" > Repository: "https://gitlab.com/shiju.jose/qemu.git"; > Branch: cxl-ras-features-2024-10-24 > > Signed-off-by: Shiju Jose <shiju.jose@xxxxxxxxxx> Similar comment to earlier on maybe using single line comments in more places rather than multiline. Perhaps worth doing that if you are respinning for other reasons. Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> > +static int cxl_mem_do_sparing_op(struct device *dev, > + struct cxl_mem_sparing_context *cxl_sparing_ctx, > + struct cxl_memdev_sparing_params *rd_params) > +{ > + struct cxl_memdev *cxlmd = cxl_sparing_ctx->cxlmd; > + struct cxl_memdev_sparing_in_payload sparing_pi; > + struct cxl_event_dram *rec = NULL; > + u16 validity_flags = 0; > + > + if (!rd_params->cap_safe_when_in_use) { > + /* > + * Memory to repair must be offline > + */ > + if (cxl_are_decoders_committed(cxlmd)) > + return -EBUSY; > + /* > + * offline, so good for repair > + */ More places as below where a single line comment would be fine and make a reader scroll a bit less. > +static int cxl_memdev_sparing_init(struct cxl_memdev *cxlmd, > + struct edac_dev_feature *ras_feature, > + const struct cxl_mem_sparing_desc *desc, > + u8 repair_inst) > +{ > + struct cxl_mem_sparing_context *cxl_sparing_ctx; > + struct cxl_memdev_sparing_params rd_params; > + struct cxl_feat_entry *feat_entry; > + int ret; > + > + feat_entry = cxl_get_feature_entry(cxlmd->cxlds, &desc->repair_uuid); > + if (IS_ERR(feat_entry)) > + return -EOPNOTSUPP; > + > + if (!(le32_to_cpu(feat_entry->flags) & CXL_FEATURE_F_CHANGEABLE)) > + return -EOPNOTSUPP; > + > + cxl_sparing_ctx = devm_kzalloc(&cxlmd->dev, sizeof(*cxl_sparing_ctx), > + GFP_KERNEL); > + if (!cxl_sparing_ctx) > + return -ENOMEM; > + > + *cxl_sparing_ctx = (struct cxl_mem_sparing_context) { > + .get_feat_size = le16_to_cpu(feat_entry->get_feat_size), > + .set_feat_size = le16_to_cpu(feat_entry->set_feat_size), > + .get_version = feat_entry->get_feat_ver, > + .set_version = feat_entry->set_feat_ver, > + .effects = le16_to_cpu(feat_entry->effects), > + .cxlmd = cxlmd, > + .repair_type = desc->repair_type, > + .granularity = desc->granularity, > + .instance = repair_inst++, > + }; > + uuid_copy(&cxl_sparing_ctx->repair_uuid, &desc->repair_uuid); > + > + /* > + * Read CXL device's sparing capabilities. a below. > + */ > + ret = cxl_mem_sparing_get_attrs(cxl_sparing_ctx, &rd_params); > + if (ret) > + return ret; > + > + /* > + * Set default value for persist_mode. > + */ If respining some of these comments don't need to be multiline.
