On Thu, Jun 9, 2016 at 11:27 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > > On Thu, Jun 9, 2016 at 10:42 AM, Yigal Korman <yigal@xxxxxxxxxxxxx> wrote: > > The 'efi_legacy_pmem' parameter will convert EFI persistent memory range > > (type 14) into E820 legacy NVDIMM (type 12) memory range. > > > > Background: > > > > In contrast with the NVDIMM E820 types where we can clearly distinguish > > between old NVDIMMs (type-12) and ACPI 6.0 NVDIMMs (type-7), the EFI > > memory types for NVDIMMs are the same before ACPI 6.0 and after > > (type-14). > > This means that old NVDIMMs under EFI aren't supported even though > > they work fine if booted with BIOS (E820). > > > > So allow the user to explicitly request the kernel to identify NVDIMMs > > as legacy under EFI. > > > > I'm concerned with the potential for this command line parameter to > collide with NFIT defined ranges. At a minimum it should confirm that > there is not already an NFIT describing the same address ranges. > That's a valid concern, but not related to this patch directly, the same might happen today when an 'memmap=XX!YY' kernel parameter collides with an NFIT on the same range. Or, albeit a far fetched scenario, a platform vendor will decide to provide an NFIT for a non-ACPI 6.0 and leave the old E820 type-12. > However, we have the ability to override / inject ACPI tables and > methods from the kernel. Why not use that facility to custom craft an > NFIT when the BIOS fails to provide one? That way EFI type-14 > maintains a constant interpretation as just a reserved memory range > with no other side effects. That might be an interesting way to implement memmap=XX!YY in general and can also replace the funny code in arch/x86/kernel/pmem.c. But, it's more complex and probably has its own caveats, this patch is simpler and straight forward, providing direct value. Thanks, Yigal -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
