nfit, libnvdimm: limited/whitelisted dimm command marshaling mechanism

There are currently 4 known similar but incompatible definitions of the command sets that can be sent to an NVDIMM through ACPI. It is also clear that future platform generations (ACPI or not) will continue to revise and extend the DIMM command set as new devices and use cases arrive. It is obviously untenable to continue to proliferate divergence of these command definitions, and to that end a standardization process has begun to provide for a unified specification. However, that leaves a problem about what to do with this first generation where vendors are already shipping divergence. The Linux kernel can support these initial diverged platforms without giving platform-firmware free reign to continue to diverge and compound kernel maintenance overhead. The kernel implementation can encourage standardization in two ways: 1/ Require that any function code that userspace wants to send be explicitly white-listed in the implementation. For ACPI this means function codes marked as supported by acpi_check_dsm() may only be invoked if they appear in the white-list. A function must be publicly documented before it is added to the white-list. 2/ The above restrictions can be trivially bypassed by using the "vendor-specific" payload command. However, since vendor-specific commands are by definition not publicly documented and have the potential to corrupt the kernel's view of the dimm state, we provide a toggle to disable vendor-specific operations. Enabling undefined behavior is a policy decision that can be made by the platform owner and encourages firmware implementations to choose public over private command implementations. Based on an initial patch from Jerry Hoemann Cc: Jerry Hoemann <jerry.hoemann@hpe.com> Cc: Christoph Hellwig <hch@infradead.org> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

DWDan Williams committed 10 years ago