forked from Minki/linux
edce21216a
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>
40 lines
875 B
C
40 lines
875 B
C
#ifndef _ASM_X86_BIOS_EBDA_H
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#define _ASM_X86_BIOS_EBDA_H
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#include <asm/io.h>
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/*
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* Returns physical address of EBDA. Returns 0 if there is no EBDA.
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*/
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static inline unsigned int get_bios_ebda(void)
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{
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/*
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* There is a real-mode segmented pointer pointing to the
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* 4K EBDA area at 0x40E.
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*/
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unsigned int address = *(unsigned short *)phys_to_virt(0x40E);
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address <<= 4;
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return address; /* 0 means none */
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}
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void reserve_bios_regions(void);
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#ifdef CONFIG_X86_CHECK_BIOS_CORRUPTION
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/*
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* This is obviously not a great place for this, but we want to be
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* able to scatter it around anywhere in the kernel.
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*/
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void check_for_bios_corruption(void);
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void start_periodic_check_for_corruption(void);
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#else
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static inline void check_for_bios_corruption(void)
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{
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}
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static inline void start_periodic_check_for_corruption(void)
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{
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}
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#endif
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#endif /* _ASM_X86_BIOS_EBDA_H */
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