| Message ID | 164740402242.3912056.8303625392871313860.stgit@dwillia2-desk3.amr.corp.intel.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | cxl/pci: Add fundamental error handling | expand |
On Tue, Mar 15, 2022 at 9:14 PM Dan Williams <dan.j.williams@intel.com> wrote: > > Add a 'struct pci_error_handlers' instance for the cxl_pci driver. > Section 8.2.5.9 "CXL RAS Capability Structure" of the CXL 2.0 > specification defines the error sources considered in this > implementation. The RAS Capability Structure defines protocol, link and > internal errors which are distinct from memory poison errors that are > conveyed via direct consumption and/or media scanning. > > The errors reported by the RAS registers are categorized into > correctable and uncorrectable errors, where the uncorrectable errors are > optionally steered to either fatal or non-fatal AER events. Table 224 > "Device Specific Error Reporting and Nomenclature Guidelines" in the CXL > 2.0 specification outlines that the remediation for uncorrectable errors > is a reset to recover. This matches how the Linux PCIe AER core treats > uncorrectable errors as occasions to reset the device to recover > operation. > > While the specification notes "CXL Reset" or "Secondary Bus Reset" as > theoretical recovery options, they are not feasible in practice since > in-flight CXL.mem operations may not terminate and cause knock-on system > fatal events. Reset is only reliable for recovering CXL.io, it is not > reliable for recovering CXL.mem. Assuming the system survives, a reset > causes CXL.mem operation to restart from scratch. > > The "ECN: Error Isolation on CXL.mem and CXL.cache" [1] document > recognizes the CXL Reset vs CXL.mem operational conflict and helps to at > least provide a mechanism for the Root Port to terminate in flight > CXL.mem operations with completions. That still poses problems in > practice if the kernel is running out of "System RAM" backed by the CXL > device and poison is used to convey the data lost to the protocol error. > > Regardless of whether the reset and restart of CXL.mem operations is > feasible / successful, the logging is still useful. So, the > implementation reads, reports, and clears the status in the RAS > Capability Structure registers, and it notifies the 'struct cxl_memdev' > associated with the given PCIe endpoint to reattach to its driver over > the reset so that the HDM decoder configuration can be reconstructed. > > The first half of the series reworks component register mapping so that > the cxl_pci driver can own the RAS Capability while the cxl_port driver > continues to own the HDM Decoder Capability. The last half implements > the RAS Capability Structure mapping and reporting via 'struct > pci_error_handlers'. > > [1]: https://www.computeexpresslink.org/spec-landing > > --- > > > Dan Williams (8): > cxl/pci: Cleanup repeated code in cxl_probe_regs() helpers > cxl/pci: Cleanup cxl_map_device_regs() > cxl/pci: Kill cxl_map_regs() > cxl/core/regs: Make cxl_map_{component,device}_regs() device generic > cxl/port: Limit the port driver to just the HDM Decoder Capability > cxl/pci: Prepare for mapping RAS Capability Structure > cxl/pci: Find and map the RAS Capability Structure > cxl/pci: Add (hopeful) error handling support > > > drivers/cxl/core/hdm.c | 33 +++++---- > drivers/cxl/core/memdev.c | 1 > drivers/cxl/core/pci.c | 3 - > drivers/cxl/core/port.c | 2 - > drivers/cxl/core/regs.c | 172 ++++++++++++++++++++++++++------------------- > drivers/cxl/cxl.h | 36 +++++++-- > drivers/cxl/cxlmem.h | 2 + > drivers/cxl/cxlpci.h | 9 -- > drivers/cxl/pci.c | 163 ++++++++++++++++++++++++++++++++----------- > 9 files changed, 273 insertions(+), 148 deletions(-) > > base-commit: 74be98774dfbc5b8b795db726bd772e735d2edd4 Apologies, wrong base-commit, this series is based on that commit + this series: https://lore.kernel.org/linux-cxl/164730733718.3806189.9721916820488234094.stgit@dwillia2-desk3.amr.corp.intel.com/
Add a 'struct pci_error_handlers' instance for the cxl_pci driver. Section 8.2.5.9 "CXL RAS Capability Structure" of the CXL 2.0 specification defines the error sources considered in this implementation. The RAS Capability Structure defines protocol, link and internal errors which are distinct from memory poison errors that are conveyed via direct consumption and/or media scanning. The errors reported by the RAS registers are categorized into correctable and uncorrectable errors, where the uncorrectable errors are optionally steered to either fatal or non-fatal AER events. Table 224 "Device Specific Error Reporting and Nomenclature Guidelines" in the CXL 2.0 specification outlines that the remediation for uncorrectable errors is a reset to recover. This matches how the Linux PCIe AER core treats uncorrectable errors as occasions to reset the device to recover operation. While the specification notes "CXL Reset" or "Secondary Bus Reset" as theoretical recovery options, they are not feasible in practice since in-flight CXL.mem operations may not terminate and cause knock-on system fatal events. Reset is only reliable for recovering CXL.io, it is not reliable for recovering CXL.mem. Assuming the system survives, a reset causes CXL.mem operation to restart from scratch. The "ECN: Error Isolation on CXL.mem and CXL.cache" [1] document recognizes the CXL Reset vs CXL.mem operational conflict and helps to at least provide a mechanism for the Root Port to terminate in flight CXL.mem operations with completions. That still poses problems in practice if the kernel is running out of "System RAM" backed by the CXL device and poison is used to convey the data lost to the protocol error. Regardless of whether the reset and restart of CXL.mem operations is feasible / successful, the logging is still useful. So, the implementation reads, reports, and clears the status in the RAS Capability Structure registers, and it notifies the 'struct cxl_memdev' associated with the given PCIe endpoint to reattach to its driver over the reset so that the HDM decoder configuration can be reconstructed. The first half of the series reworks component register mapping so that the cxl_pci driver can own the RAS Capability while the cxl_port driver continues to own the HDM Decoder Capability. The last half implements the RAS Capability Structure mapping and reporting via 'struct pci_error_handlers'. [1]: https://www.computeexpresslink.org/spec-landing --- Dan Williams (8): cxl/pci: Cleanup repeated code in cxl_probe_regs() helpers cxl/pci: Cleanup cxl_map_device_regs() cxl/pci: Kill cxl_map_regs() cxl/core/regs: Make cxl_map_{component,device}_regs() device generic cxl/port: Limit the port driver to just the HDM Decoder Capability cxl/pci: Prepare for mapping RAS Capability Structure cxl/pci: Find and map the RAS Capability Structure cxl/pci: Add (hopeful) error handling support drivers/cxl/core/hdm.c | 33 +++++---- drivers/cxl/core/memdev.c | 1 drivers/cxl/core/pci.c | 3 - drivers/cxl/core/port.c | 2 - drivers/cxl/core/regs.c | 172 ++++++++++++++++++++++++++------------------- drivers/cxl/cxl.h | 36 +++++++-- drivers/cxl/cxlmem.h | 2 + drivers/cxl/cxlpci.h | 9 -- drivers/cxl/pci.c | 163 ++++++++++++++++++++++++++++++++----------- 9 files changed, 273 insertions(+), 148 deletions(-) base-commit: 74be98774dfbc5b8b795db726bd772e735d2edd4