RE: [PATCH v2] lsefimmap: support persistent memory and other UEFI 2.5 features

[Elliott, Robert (Persistent Memory)]

> -----Original Message-----
> From: address@hidden [mailto:grub-devel-
> address@hidden On Behalf Of Andrei Borzenkov
> Sent: Thursday, December 17, 2015 12:06 PM
> To: address@hidden
> Subject: Re: [PATCH v2] lsefimmap: support persistent memory and other
> UEFI 2.5 features
> 
> > 2. Decode the memory attributes that were added in UEFI 2.5:
> > * NV (non-volatile)
> 
> Out of curiosity - what is the difference between this and persistent?
> They sound mostly the same to me.

Good question, and one that we've been revisiting as we ponder
ways to workaround the bug in grub-2.00 to 2.02 that mapped
EfiPersistentMemory (type 14) into E820 AddressRangeMemory
(type 1).

One difference is that the NV attribute can be reported with
any type.  It could be reported with EfiConventionalMemory,
EfiReservedMemoryType, EfiPalCode, etc.

For example, the NV attribute could be defined as meaning that 
the OS should not save and restore that region during the S4
sleep state, even if it's a region like EfiConventionalMemory
for which that is normally required, because hardware already
does so (it's not defined that way yet, but could be).

We're contemplating reporting persistent memory as:
    EfiReservedMemoryType with the NV attribute
rather than EfiPersistentMemory, which appears safe for 
all versions of grub.

---
Robert Elliott, HPE Persistent Memory