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7c10093692
On non-BIOS platforms it is possible that the BIOS data area contains garbage instead of being zeroed or something equivalent (firmware people: we are talking of 1.5K here, so please do the sane thing.) We need on the order of 20-30K of low memory in order to boot, which may grow up to < 64K in the future. We probably want to avoid the lowest of the low memory. At the same time, it seems extremely unlikely that a legitimate EBDA would ever reach down to the 128K (which would require it to be over half a megabyte in size.) Thus, pick 128K as the cutoff for "this is insane, ignore." We may still end up reserving a bunch of extra memory on the low megabyte, but that is not really a major issue these days. In the worst case we lose 512K of RAM. This code really should be merged with trim_bios_range() in arch/x86/kernel/setup.c, but that is a bigger patch for a later merge window. Reported-by: Darren Hart <dvhart@linux.intel.com> Signed-off-by: H. Peter Anvin <hpa@linux.intel.com> Cc: Matt Fleming <matt.fleming@intel.com> Cc: <stable@vger.kernel.org> Link: http://lkml.kernel.org/n/tip-oebml055yyfm8yxmria09rja@git.kernel.org
72 lines
2.2 KiB
C
72 lines
2.2 KiB
C
#include <linux/kernel.h>
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#include <linux/init.h>
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#include <linux/memblock.h>
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#include <asm/setup.h>
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#include <asm/bios_ebda.h>
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/*
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* The BIOS places the EBDA/XBDA at the top of conventional
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* memory, and usually decreases the reported amount of
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* conventional memory (int 0x12) too. This also contains a
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* workaround for Dell systems that neglect to reserve EBDA.
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* The same workaround also avoids a problem with the AMD768MPX
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* chipset: reserve a page before VGA to prevent PCI prefetch
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* into it (errata #56). Usually the page is reserved anyways,
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* unless you have no PS/2 mouse plugged in.
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*
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* This functions is deliberately very conservative. Losing
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* memory in the bottom megabyte is rarely a problem, as long
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* as we have enough memory to install the trampoline. Using
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* memory that is in use by the BIOS or by some DMA device
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* the BIOS didn't shut down *is* a big problem.
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*/
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#define BIOS_LOWMEM_KILOBYTES 0x413
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#define LOWMEM_CAP 0x9f000U /* Absolute maximum */
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#define INSANE_CUTOFF 0x20000U /* Less than this = insane */
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void __init reserve_ebda_region(void)
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{
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unsigned int lowmem, ebda_addr;
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/*
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* To determine the position of the EBDA and the
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* end of conventional memory, we need to look at
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* the BIOS data area. In a paravirtual environment
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* that area is absent. We'll just have to assume
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* that the paravirt case can handle memory setup
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* correctly, without our help.
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*/
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if (paravirt_enabled())
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return;
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/* end of low (conventional) memory */
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lowmem = *(unsigned short *)__va(BIOS_LOWMEM_KILOBYTES);
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lowmem <<= 10;
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/* start of EBDA area */
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ebda_addr = get_bios_ebda();
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/*
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* Note: some old Dells seem to need 4k EBDA without
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* reporting so, so just consider the memory above 0x9f000
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* to be off limits (bugzilla 2990).
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*/
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/* If the EBDA address is below 128K, assume it is bogus */
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if (ebda_addr < INSANE_CUTOFF)
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ebda_addr = LOWMEM_CAP;
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/* If lowmem is less than 128K, assume it is bogus */
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if (lowmem < INSANE_CUTOFF)
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lowmem = LOWMEM_CAP;
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/* Use the lower of the lowmem and EBDA markers as the cutoff */
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lowmem = min(lowmem, ebda_addr);
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lowmem = min(lowmem, LOWMEM_CAP); /* Absolute cap */
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/* reserve all memory between lowmem and the 1MB mark */
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memblock_reserve(lowmem, 0x100000 - lowmem);
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}
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