What: /sys/kernel/debug/cxl/memX/inject_poison Date: April, 2023 KernelVersion: v6.4 Contact: linux-cxl@vger.kernel.org Description: (WO) When a Device Physical Address (DPA) is written to this attribute, the memdev driver sends an inject poison command to the device for the specified address. The DPA must be 64-byte aligned and the length of the injected poison is 64-bytes. If successful, the device returns poison when the address is accessed through the CXL.mem bus. Injecting poison adds the address to the device's Poison List and the error source is set to Injected. In addition, the device adds a poison creation event to its internal Informational Event log, updates the Event Status register, and if configured, interrupts the host. It is not an error to inject poison into an address that already has poison present and no error is returned. If the device returns 'Inject Poison Limit Reached' an -EBUSY error is returned to the user. The inject_poison attribute is only visible for devices supporting the capability. TEST-ONLY INTERFACE: This interface is intended for testing and validation purposes only. It is not a data repair mechanism and should never be used on production systems or live data. DATA LOSS RISK: For CXL persistent memory (PMEM) devices, poison injection can result in permanent data loss. Injected poison may render data permanently inaccessible even after clearing, as the clear operation writes zeros and does not recover original data. SYSTEM STABILITY RISK: For volatile memory, poison injection can cause kernel crashes, system instability, or unpredictable behavior if the poisoned addresses are accessed by running code or critical kernel structures. What: /sys/kernel/debug/cxl/memX/clear_poison Date: April, 2023 KernelVersion: v6.4 Contact: linux-cxl@vger.kernel.org Description: (WO) When a Device Physical Address (DPA) is written to this attribute, the memdev driver sends a clear poison command to the device for the specified address. Clearing poison removes the address from the device's Poison List and writes 0 (zero) for 64 bytes starting at address. It is not an error to clear poison from an address that does not have poison set. If the device cannot clear poison from the address, -ENXIO is returned. The clear_poison attribute is only visible for devices supporting the capability. TEST-ONLY INTERFACE: This interface is intended for testing and validation purposes only. It is not a data repair mechanism and should never be used on production systems or live data. CLEAR IS NOT DATA RECOVERY: This operation writes zeros to the specified address range and removes the address from the poison list. It does NOT recover or restore original data that may have been present before poison injection. Any original data at the cleared address is permanently lost and replaced with zeros. CLEAR IS NOT A REPAIR MECHANISM: This interface is for testing purposes only and should not be used as a data repair tool. Clearing poison is fundamentally different from data recovery or error correction. What: /sys/kernel/debug/cxl/regionX/inject_poison Date: August, 2025 Contact: linux-cxl@vger.kernel.org Description: (WO) When a Host Physical Address (HPA) is written to this attribute, the region driver translates it to a Device Physical Address (DPA) and identifies the corresponding memdev. It then sends an inject poison command to that memdev at the translated DPA. Refer to the memdev ABI entry at: /sys/kernel/debug/cxl/memX/inject_poison for the detailed behavior. This attribute is only visible if all memdevs participating in the region support both inject and clear poison commands. TEST-ONLY INTERFACE: This interface is intended for testing and validation purposes only. It is not a data repair mechanism and should never be used on production systems or live data. DATA LOSS RISK: For CXL persistent memory (PMEM) devices, poison injection can result in permanent data loss. Injected poison may render data permanently inaccessible even after clearing, as the clear operation writes zeros and does not recover original data. SYSTEM STABILITY RISK: For volatile memory, poison injection can cause kernel crashes, system instability, or unpredictable behavior if the poisoned addresses are accessed by running code or critical kernel structures. What: /sys/kernel/debug/cxl/regionX/clear_poison Date: August, 2025 Contact: linux-cxl@vger.kernel.org Description: (WO) When a Host Physical Address (HPA) is written to this attribute, the region driver translates it to a Device Physical Address (DPA) and identifies the corresponding memdev. It then sends a clear poison command to that memdev at the translated DPA. Refer to the memdev ABI entry at: /sys/kernel/debug/cxl/memX/clear_poison for the detailed behavior. This attribute is only visible if all memdevs participating in the region support both inject and clear poison commands. TEST-ONLY INTERFACE: This interface is intended for testing and validation purposes only. It is not a data repair mechanism and should never be used on production systems or live data. CLEAR IS NOT DATA RECOVERY: This operation writes zeros to the specified address range and removes the address from the poison list. It does NOT recover or restore original data that may have been present before poison injection. Any original data at the cleared address is permanently lost and replaced with zeros. CLEAR IS NOT A REPAIR MECHANISM: This interface is for testing purposes only and should not be used as a data repair tool. Clearing poison is fundamentally different from data recovery or error correction. What: /sys/kernel/debug/cxl/einj_types Date: January, 2024 KernelVersion: v6.9 Contact: linux-cxl@vger.kernel.org Description: (RO) Prints the CXL protocol error types made available by the platform in the format: 0x The possible error types are (as of ACPI v6.5): 0x1000 CXL.cache Protocol Correctable 0x2000 CXL.cache Protocol Uncorrectable non-fatal 0x4000 CXL.cache Protocol Uncorrectable fatal 0x8000 CXL.mem Protocol Correctable 0x10000 CXL.mem Protocol Uncorrectable non-fatal 0x20000 CXL.mem Protocol Uncorrectable fatal The can be written to einj_inject to inject into a chosen dport. What: /sys/kernel/debug/cxl/$dport_dev/einj_inject Date: January, 2024 KernelVersion: v6.9 Contact: linux-cxl@vger.kernel.org Description: (WO) Writing an integer to this file injects the corresponding CXL protocol error into $dport_dev ($dport_dev will be a device name from /sys/bus/pci/devices). The integer to type mapping for injection can be found by reading from einj_types. If the dport was enumerated in RCH mode, a CXL 1.1 error is injected, otherwise a CXL 2.0 error is injected.