question about reserve_bios_regions

From: Cao jin
Date: Fri Jan 04 2019 - 02:35:11 EST


I am looking into these code via find_trampoline_placement, and I have
some questions still not clear after lots of investigation, hope to get
some hints.

1. How is the value of BIOS_START_MIN(128k) determined? I don't find any
clue about it until now.

2. BIOS_START_MAX is define as 0x9f000U(636k), but both the comments say
640k, is that a quirk or just typo? I thought the 4k difference is the
quirk, but later I guess the real quirk lies in latter judgment of :

if (ebda_start >= BIOS_START_MIN && ebda_start < bios_start)

I have checked out commit edce21216a8: ("x86/boot: Reorganize and clean
up the BIOS area reservation code"), still no clue.

Cao jin