UEFI stands for "Unified Extensible Firmware Interface", where "Firmware"
is an ancient African word meaning "Why do something right when you can
do it so wrong that children will weep and brave adults will cower before
you", and "UEI" is Celtic for "We missed DOS so we burned it into your
ROMs". The UEFI specification provides for runtime services (ie, another
way for the operating system to be forced to depend on the firmware) and
we rely on these for certain trivial tasks such as setting up the
bootloader. But some hardware fails to work if we attempt to use these
runtime services from physical mode, and so we have to switch into virtual
mode. So far so dreadful.
"UEI" is Celtic for "We missed DOS so we burned it into your ROMS"
I love it "maith an fear"
There are currently only two situations where we need to map EFI Boot
Service regions,
1. To workaround the firmware bug described in 916f676f8
2. To access the ACPI BGRT image
but since we haven't seen an i386 implementation that requires either,
this simple fix should suffice for now. Item 2. above does still work on
i386 provided that the BGRT image is not in highmem.
Matt, Peter, Josh, Darren.
Given it's not possible to guarantee someone won't stuff a BGRT into
EFI_BOOT_MEMORY >= highmem eventually (and indeed the axioms of the
universe pretty much guarantee eventually it will be so) - I'd suggest
version 2.
A kernel parameter - rather than a probe for BGRT - since we anticipate
BIOS bugs on the way.
Version 2 of the submitted path introduces an early kernel parameter
"virt_mapboot" - which is true by default (maintaining the current
behavior of mapping EFI_BOOT_MEMORY by default) - but which can be set
to false - if your IA32 BIOS is not buggy.
Perhaps it would be better to be optimistic.
Change the behavior of efi_enter_virtual_mode() to do the right thing
re: the standard and require passing of a parameter to switch on
work-arounds for non-standards conformant BIOS. Note: this approach
would break BGRT code - requiring addition of kernel parameters to
existing systems - which from a user-friendliness POV is probably
verboten....
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