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#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/memblock.h>
#include <asm/setup.h>
#include <asm/bios_ebda.h>
/*
* The BIOS places the EBDA/XBDA at the top of conventional
* memory, and usually decreases the reported amount of
* conventional memory (int 0x12) too. This also contains a
* workaround for Dell systems that neglect to reserve EBDA.
* The same workaround also avoids a problem with the AMD768MPX
* chipset: reserve a page before VGA to prevent PCI prefetch
* into it (errata #56). Usually the page is reserved anyways,
* unless you have no PS/2 mouse plugged in.
*
* This functions is deliberately very conservative. Losing
* memory in the bottom megabyte is rarely a problem, as long
* as we have enough memory to install the trampoline. Using
* memory that is in use by the BIOS or by some DMA device
* the BIOS didn't shut down *is* a big problem.
*/
#define BIOS_LOWMEM_KILOBYTES 0x413
#define LOWMEM_CAP 0x9f000U /* Absolute maximum */
#define INSANE_CUTOFF 0x20000U /* Less than this = insane */
void __init reserve_ebda_region(void)
{
unsigned int lowmem, ebda_addr;
/*
* To determine the position of the EBDA and the
* end of conventional memory, we need to look at
* the BIOS data area. In a paravirtual environment
* that area is absent. We'll just have to assume
* that the paravirt case can handle memory setup
* correctly, without our help.
*/
if (paravirt_enabled())
return;
/* end of low (conventional) memory */
lowmem = *(unsigned short *)__va(BIOS_LOWMEM_KILOBYTES);
lowmem <<= 10;
/* start of EBDA area */
ebda_addr = get_bios_ebda();
/*
* Note: some old Dells seem to need 4k EBDA without
* reporting so, so just consider the memory above 0x9f000
* to be off limits (bugzilla 2990).
*/
/* If the EBDA address is below 128K, assume it is bogus */
if (ebda_addr < INSANE_CUTOFF)
ebda_addr = LOWMEM_CAP;
/* If lowmem is less than 128K, assume it is bogus */
if (lowmem < INSANE_CUTOFF)
lowmem = LOWMEM_CAP;
/* Use the lower of the lowmem and EBDA markers as the cutoff */
lowmem = min(lowmem, ebda_addr);
lowmem = min(lowmem, LOWMEM_CAP); /* Absolute cap */
/* reserve all memory between lowmem and the 1MB mark */
memblock_reserve(lowmem, 0x100000 - lowmem);
}
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