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authorIngo Molnar <mingo@kernel.org>2016-07-21 10:53:52 +0300
committerIngo Molnar <mingo@kernel.org>2016-07-21 11:11:57 +0300
commitedce21216a8887bf06ba85ee49a00695e44c4341 (patch)
tree79c6f03710dbe0dd983715f727691fcf2950309b /arch/x86/kernel/head64.c
parent4ff5308744f5858e4e49e56a0445e2f8b73e47e0 (diff)
downloadlinux-edce21216a8887bf06ba85ee49a00695e44c4341.tar.xz
x86/boot: Reorganize and clean up the BIOS area reservation code
So the reserve_ebda_region() code has accumulated a number of problems over the years that make it really difficult to read and understand: - The calculation of 'lowmem' and 'ebda_addr' is an unnecessarily interleaved mess of first lowmem, then ebda_addr, then lowmem tweaks... - 'lowmem' here means 'super low mem' - i.e. 16-bit addressable memory. In other parts of the x86 code 'lowmem' means 32-bit addressable memory... This makes it super confusing to read. - It does not help at all that we have various memory range markers, half of which are 'start of range', half of which are 'end of range' - but this crucial property is not obvious in the naming at all ... gave me a headache trying to understand all this. - Also, the 'ebda_addr' name sucks: it highlights that it's an address (which is obvious, all values here are addresses!), while it does not highlight that it's the _start_ of the EBDA region ... - 'BIOS_LOWMEM_KILOBYTES' says a lot of things, except that this is the only value that is a pointer to a value, not a memory range address! - The function name itself is a misnomer: it says 'reserve_ebda_region()' while its main purpose is to reserve all the firmware ROM typically between 640K and 1MB, while the 'EBDA' part is only a small part of that ... - Likewise, the paravirt quirk flag name 'ebda_search' is misleading as well: this too should be about whether to reserve firmware areas in the paravirt case. - In fact thinking about this as 'end of RAM' is confusing: what this function *really* wants to reserve is firmware data and code areas! Once the thinking is inverted from a mixed 'ram' and 'reserved firmware area' notion to a pure 'reserved area' notion everything becomes a lot clearer. To improve all this rewrite the whole code (without changing the logic): - Firstly invert the naming from 'lowmem end' to 'BIOS reserved area start' and propagate this concept through all the variable names and constants. BIOS_RAM_SIZE_KB_PTR // was: BIOS_LOWMEM_KILOBYTES BIOS_START_MIN // was: INSANE_CUTOFF ebda_start // was: ebda_addr bios_start // was: lowmem BIOS_START_MAX // was: LOWMEM_CAP - Then clean up the name of the function itself by renaming it to reserve_bios_regions() and renaming the ::ebda_search paravirt flag to ::reserve_bios_regions. - Fix up all the comments (fix typos), harmonize and simplify their formulation and remove comments that become unnecessary due to the much better naming all around. Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/kernel/head64.c')
-rw-r--r--arch/x86/kernel/head64.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index b72fb0b71dd1..99d48e7d2974 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -183,7 +183,7 @@ void __init x86_64_start_reservations(char *real_mode_data)
copy_bootdata(__va(real_mode_data));
x86_early_init_platform_quirks();
- reserve_ebda_region();
+ reserve_bios_regions();
switch (boot_params.hdr.hardware_subarch) {
case X86_SUBARCH_INTEL_MID: