[pcbios] Support arbitrary splits of the e820 memory map
Allow for an arbitrary number of splits of the system memory map via
INT 15,e820.
Features of the new map-mangling algorithm include:
Supports random access to e820 map entries.
Requires only sequential access support from the underlying e820
map, even if our caller uses random access.
Empty regions will always be stripped.
Always terminates with %ebx=0, even if the underlying map terminates
with CF=1.
Allows for an arbitrary number of hidden regions, with underlying
regions split into as many subregions as necessary.
Total size increase to achieve this is 193 bytes.
[pcbios] Prepare for multiple splits of hidden e820 memory regions
Define a list of N allowed memory regions, and split each underlying
e820 region into up to N subregions. Strip resulting empty regions
out of the map, avoiding using the "return with CF set to strip last
empty region" trick, because it seems that bootmgr.exe in Win2k8 gets
upset if the memory map is terminated with CF set.
This is an intermediate checkin that defines a single allowed memory
region covering the entire 64-bit address space, and uses the existing
map-mangling code on top of the new region-splitting code. This
sanitises the memory map to the point that Win2k8 is able to boot even
on a system that defines a final zero-length region at the 4GB mark.
I'm checking this in because it may be useful for future debugging
efforts to be able to run with the existing and known-working map
mangling code together with the map sanitisation capabilities of the
new map mangling code.
Ensure that empty e820 regions are skipped even at the end of the
memory map. (We achieve this by setting CF on the last entry if it is
zero-length; this avoids the need to look ahead to see at each entry
if the *next* entry would be both the last entry and zero-length).
This fixes the "0kB base memory" error message upon starting Windows
2003 on a SunFire X2100.
Ensure that empty e820 regions are skipped even at the end of the
memory map. (We achieve this by setting CF on the last entry if it is
zero-length; this avoids the need to look ahead to see at each entry
if the *next* entry would be both the last entry and zero-length).
This fixes the "0kB base memory" error message upon starting Windows
2003 on a SunFire X2100.
Check to see if we've reached the end of the map before attempting to
skip past an empty region, otherwise we end up generating an infinitely
long e820 map. (Yes, there *are* real systems that provide e820 maps
with a zero-length region at the end...)
We now split e820 regions around ourselves, rather than just
truncating the e820 region. This avoids the worst-case scenario of
losing all memory over 4GB.
It's more important to get the memory map right now that we're
expecting to still be loaded when the OS starts in several situations
(e.g. Linux with UNDI driver, any OS with iSCSI/AoE boot, etc.).
Michael Brown