Questions about PVH memory layout

[joshua_peter@xxxxxx]

Hello everyone,

I hope this is the right forum for these kinds of questions (the website
states no "technical support queries"; I'm not sure if this qualifies).
If not, sorry for the disturbance; just simply direct me elsewhere then.

Anyway, I'm currently trying to get into how Xen works in detail, so
for one I've been reading a lot of code, but also I dumped the P2M table
of my PVH guest to get a feel for how things are layed out in memory. I
mean there is the usual stuff, such as lots of RAM, and the APIC is
mapped at 0xFEE00000 and the APCI tables at 0xFC000000 onwards. But two
things stuck out to me, which for the life of me I couldn't figure out
from just reading the code. The first one is, there are a few pages at
the end of the 32bit address space (from 0xFEFF8000 to 0xFEFFF000),
which according to the E820 is declared simply as "reserved". The other
thing is, the first 512 pages at the beginning of the address space are
mapped linearly, which usually leads to them being mapped as a single
2MB pages. But there is this one page at 0x00001000 that sticks out
completely. By that I mean (to make things more concrete), in my PVH
guest the page at 0x00000000 maps to 0x13C200000, 0x00002000 maps to
0x13C202000, 0x00003000 maps to 0x13C203000, etc. But 0x00001000 maps
to 0xB8DBD000, which seems very odd to me (at least from simply looking
at the addresses). My initial guess was that this is some bootloader
related stuff, but Google didn't show up any info related to that
memory area, and most of the x86/PC boot stuff seems to happen below
the 0x1000 mark.

Would someone be so kind to tell me what those two things are? Many
thanks in advance.

(Btw. I'm running Xen 4.13.1 on Intel x64, booting my PVH guest with
PyGRUB, if it's relevant.)

Best regards,
Peter