| 1 | |
| 2 | #include <linux/kernel.h>
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| 3 | #include <linux/init.h>
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| 4 | #include <linux/memblock.h>
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| 5 |
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| 6 | #include <asm/setup.h>
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| 7 | #include <asm/bios_ebda.h>
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| 8 |
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| 9 | |
| 10 | * This function reserves all conventional PC system BIOS related
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| 11 | * firmware memory areas (some of which are data, some of which
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| 12 | * are code), that must not be used by the kernel as available
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| 13 | * RAM.
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| 14 | *
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| 15 | * The BIOS places the EBDA/XBDA at the top of conventional
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| 16 | * memory, and usually decreases the reported amount of
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| 17 | * conventional memory (int 0x12) too.
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| 18 | *
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| 19 | * This means that as a first approximation on most systems we can
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| 20 | * guess the reserved BIOS area by looking at the low BIOS RAM size
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| 21 | * value and assume that everything above that value (up to 1MB) is
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| 22 | * reserved.
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| 23 | *
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| 24 | * But life in firmware country is not that simple:
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| 25 | *
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| 26 | * - This code also contains a quirk for Dell systems that neglect
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| 27 | * to reserve the EBDA area in the 'RAM size' value ...
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| 28 | *
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| 29 | * - The same quirk also avoids a problem with the AMD768MPX
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| 30 | * chipset: reserve a page before VGA to prevent PCI prefetch
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| 31 | * into it (errata #56). (Usually the page is reserved anyways,
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| 32 | * unless you have no PS/2 mouse plugged in.)
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| 33 | *
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| 34 | * - Plus paravirt systems don't have a reliable value in the
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| 35 | * 'BIOS RAM size' pointer we can rely on, so we must quirk
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| 36 | * them too.
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| 37 | *
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| 38 | * Due to those various problems this function is deliberately
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| 39 | * very conservative and tries to err on the side of reserving
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| 40 | * too much, to not risk reserving too little.
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| 41 | *
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| 42 | * Losing a small amount of memory in the bottom megabyte is
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| 43 | * rarely a problem, as long as we have enough memory to install
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| 44 | * the SMP bootup trampoline which *must* be in this area.
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| 45 | *
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| 46 | * Using memory that is in use by the BIOS or by some DMA device
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| 47 | * the BIOS didn't shut down *is* a big problem to the kernel,
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| 48 | * obviously.
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| 49 |
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| 50 |
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| 51 | #define BIOS_RAM_SIZE_KB_PTR 0x413
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| 52 |
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| 53 | #define BIOS_START_MIN 0x20000U
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| 54 | #define BIOS_START_MAX 0x9f000U
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| 55 |
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| 56 | void __init reserve_bios_regions(void)
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| 57 | {
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| 58 | unsigned int bios_start, ebda_start;
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| 59 |
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| 60 | |
| 61 | * NOTE: In a paravirtual environment the BIOS reserved
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| 62 | * area is absent. We'll just have to assume that the
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| 63 | * paravirt case can handle memory setup correctly,
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| 64 | * without our help.
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| 65 |
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| 66 | if (!x86_platform.legacy.reserve_bios_regions)
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| 67 | return;
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| 68 |
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| 69 | |
| 70 | * BIOS RAM size is encoded in kilobytes, convert it
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| 71 | * to bytes to get a first guess at where the BIOS
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| 72 | * firmware area starts:
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| 73 |
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| 74 | bios_start = *(unsigned short *)__va(BIOS_RAM_SIZE_KB_PTR);
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| 75 | bios_start <<= 10;
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| 76 |
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| 77 | |
| 78 | * If bios_start is less than 128K, assume it is bogus
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| 79 | * and bump it up to 640K. Similarly, if bios_start is above 640K,
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| 80 | * don't trust it.
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| 81 |
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| 82 | if (bios_start < BIOS_START_MIN || bios_start > BIOS_START_MAX)
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| 83 | bios_start = BIOS_START_MAX;
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| 84 |
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| 85 |
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| 86 | ebda_start = get_bios_ebda();
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| 87 |
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| 88 | |
| 89 | * If the EBDA start address is sane and is below the BIOS region,
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| 90 | * then also reserve everything from the EBDA start address up to
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| 91 | * the BIOS region.
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| 92 |
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| 93 | if (ebda_start >= BIOS_START_MIN && ebda_start < bios_start)
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| 94 | bios_start = ebda_start;
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| 95 |
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| 96 |
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| 97 | memblock_reserve(bios_start, 0x100000 - bios_start);
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| 98 | }
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