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A "DPA invalidation event" is any scenario where the contents of a DPA (Device Physical Address) is modified in a way that is incoherent with CPU caches, or if the HPA (Host Physical Address) to DPA association changes due to a remapping event. PMEM security events like Unlock and Passphrase Secure Erase already manage caches through LIBNVDIMM, so that leaves HPA to DPA remap events that need cache management by the CXL core. Those only happen when the boot time CXL configuration has changed. That event occurs when userspace attaches an endpoint decoder to a region configuration, and that region is subsequently activated. The implications of not invalidating caches between remap events is that reads from the region at different points in time may return different results due to stale cached data from the previous HPA to DPA mapping. Without a guarantee that the region contents after cxl_region_probe() are written before being read (a layering-violation assumption that cxl_region_probe() can not make) the CXL subsystem needs to ensure that reads that precede writes see consistent results. A CONFIG_CXL_REGION_INVALIDATION_TEST option is added to support debug and unit testing of the CXL implementation in QEMU or other environments where cpu_cache_has_invalidate_memregion() returns false. This may prove too restrictive for QEMU where the HDM decoders are emulated, but in that case the CXL subsystem needs some new mechanism / indication that the HDM decoder is emulated and not a passthrough of real hardware. Reviewed-by: Dave Jiang <dave.jiang@intel.com> Link: https://lore.kernel.org/r/166993222098.1995348.16604163596374520890.stgit@dwillia2-xfh.jf.intel.com Signed-off-by: Dan Williams <dan.j.williams@intel.com>
133 lines
4.9 KiB
Plaintext
133 lines
4.9 KiB
Plaintext
# SPDX-License-Identifier: GPL-2.0-only
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menuconfig CXL_BUS
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tristate "CXL (Compute Express Link) Devices Support"
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depends on PCI
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select PCI_DOE
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help
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CXL is a bus that is electrically compatible with PCI Express, but
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layers three protocols on that signalling (CXL.io, CXL.cache, and
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CXL.mem). The CXL.cache protocol allows devices to hold cachelines
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locally, the CXL.mem protocol allows devices to be fully coherent
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memory targets, the CXL.io protocol is equivalent to PCI Express.
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Say 'y' to enable support for the configuration and management of
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devices supporting these protocols.
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if CXL_BUS
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config CXL_PCI
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tristate "PCI manageability"
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default CXL_BUS
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help
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The CXL specification defines a "CXL memory device" sub-class in the
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PCI "memory controller" base class of devices. Device's identified by
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this class code provide support for volatile and / or persistent
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memory to be mapped into the system address map (Host-managed Device
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Memory (HDM)).
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Say 'y/m' to enable a driver that will attach to CXL memory expander
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devices enumerated by the memory device class code for configuration
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and management primarily via the mailbox interface. See Chapter 2.3
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Type 3 CXL Device in the CXL 2.0 specification for more details.
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If unsure say 'm'.
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config CXL_MEM_RAW_COMMANDS
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bool "RAW Command Interface for Memory Devices"
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depends on CXL_PCI
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help
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Enable CXL RAW command interface.
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The CXL driver ioctl interface may assign a kernel ioctl command
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number for each specification defined opcode. At any given point in
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time the number of opcodes that the specification defines and a device
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may implement may exceed the kernel's set of associated ioctl function
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numbers. The mismatch is either by omission, specification is too new,
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or by design. When prototyping new hardware, or developing / debugging
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the driver it is useful to be able to submit any possible command to
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the hardware, even commands that may crash the kernel due to their
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potential impact to memory currently in use by the kernel.
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If developing CXL hardware or the driver say Y, otherwise say N.
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config CXL_ACPI
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tristate "CXL ACPI: Platform Support"
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depends on ACPI
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default CXL_BUS
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select ACPI_TABLE_LIB
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help
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Enable support for host managed device memory (HDM) resources
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published by a platform's ACPI CXL memory layout description. See
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Chapter 9.14.1 CXL Early Discovery Table (CEDT) in the CXL 2.0
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specification, and CXL Fixed Memory Window Structures (CEDT.CFMWS)
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(https://www.computeexpresslink.org/spec-landing). The CXL core
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consumes these resource to publish the root of a cxl_port decode
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hierarchy to map regions that represent System RAM, or Persistent
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Memory regions to be managed by LIBNVDIMM.
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If unsure say 'm'.
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config CXL_PMEM
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tristate "CXL PMEM: Persistent Memory Support"
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depends on LIBNVDIMM
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default CXL_BUS
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help
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In addition to typical memory resources a platform may also advertise
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support for persistent memory attached via CXL. This support is
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managed via a bridge driver from CXL to the LIBNVDIMM system
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subsystem. Say 'y/m' to enable support for enumerating and
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provisioning the persistent memory capacity of CXL memory expanders.
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If unsure say 'm'.
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config CXL_MEM
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tristate "CXL: Memory Expansion"
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depends on CXL_PCI
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default CXL_BUS
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help
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The CXL.mem protocol allows a device to act as a provider of "System
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RAM" and/or "Persistent Memory" that is fully coherent as if the
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memory were attached to the typical CPU memory controller. This is
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known as HDM "Host-managed Device Memory".
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Say 'y/m' to enable a driver that will attach to CXL.mem devices for
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memory expansion and control of HDM. See Chapter 9.13 in the CXL 2.0
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specification for a detailed description of HDM.
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If unsure say 'm'.
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config CXL_PORT
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default CXL_BUS
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tristate
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config CXL_SUSPEND
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def_bool y
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depends on SUSPEND && CXL_MEM
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config CXL_REGION
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bool
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default CXL_BUS
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# For MAX_PHYSMEM_BITS
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depends on SPARSEMEM
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select MEMREGION
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select GET_FREE_REGION
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config CXL_REGION_INVALIDATION_TEST
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bool "CXL: Region Cache Management Bypass (TEST)"
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depends on CXL_REGION
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help
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CXL Region management and security operations potentially invalidate
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the content of CPU caches without notifiying those caches to
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invalidate the affected cachelines. The CXL Region driver attempts
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to invalidate caches when those events occur. If that invalidation
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fails the region will fail to enable. Reasons for cache
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invalidation failure are due to the CPU not providing a cache
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invalidation mechanism. For example usage of wbinvd is restricted to
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bare metal x86. However, for testing purposes toggling this option
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can disable that data integrity safety and proceed with enabling
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regions when there might be conflicting contents in the CPU cache.
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If unsure, or if this kernel is meant for production environments,
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say N.
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endif
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