mirror of https://gitee.com/openkylin/linux.git
98 lines
3.1 KiB
C
98 lines
3.1 KiB
C
#include <linux/kernel.h>
|
|
#include <linux/init.h>
|
|
#include <linux/memblock.h>
|
|
|
|
#include <asm/setup.h>
|
|
#include <asm/bios_ebda.h>
|
|
|
|
/*
|
|
* This function reserves all conventional PC system BIOS related
|
|
* firmware memory areas (some of which are data, some of which
|
|
* are code), that must not be used by the kernel as available
|
|
* RAM.
|
|
*
|
|
* 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 means that as a first approximation on most systems we can
|
|
* guess the reserved BIOS area by looking at the low BIOS RAM size
|
|
* value and assume that everything above that value (up to 1MB) is
|
|
* reserved.
|
|
*
|
|
* But life in firmware country is not that simple:
|
|
*
|
|
* - This code also contains a quirk for Dell systems that neglect
|
|
* to reserve the EBDA area in the 'RAM size' value ...
|
|
*
|
|
* - The same quirk 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.)
|
|
*
|
|
* - Plus paravirt systems don't have a reliable value in the
|
|
* 'BIOS RAM size' pointer we can rely on, so we must quirk
|
|
* them too.
|
|
*
|
|
* Due to those various problems this function is deliberately
|
|
* very conservative and tries to err on the side of reserving
|
|
* too much, to not risk reserving too little.
|
|
*
|
|
* Losing a small amount of memory in the bottom megabyte is
|
|
* rarely a problem, as long as we have enough memory to install
|
|
* the SMP bootup trampoline which *must* be in this area.
|
|
*
|
|
* Using memory that is in use by the BIOS or by some DMA device
|
|
* the BIOS didn't shut down *is* a big problem to the kernel,
|
|
* obviously.
|
|
*/
|
|
|
|
#define BIOS_RAM_SIZE_KB_PTR 0x413
|
|
|
|
#define BIOS_START_MIN 0x20000U /* 128K, less than this is insane */
|
|
#define BIOS_START_MAX 0x9f000U /* 640K, absolute maximum */
|
|
|
|
void __init reserve_bios_regions(void)
|
|
{
|
|
unsigned int bios_start, ebda_start;
|
|
|
|
/*
|
|
* NOTE: In a paravirtual environment the BIOS reserved
|
|
* area is absent. We'll just have to assume that the
|
|
* paravirt case can handle memory setup correctly,
|
|
* without our help.
|
|
*/
|
|
if (!x86_platform.legacy.reserve_bios_regions)
|
|
return;
|
|
|
|
/*
|
|
* BIOS RAM size is encoded in kilobytes, convert it
|
|
* to bytes to get a first guess at where the BIOS
|
|
* firmware area starts:
|
|
*/
|
|
bios_start = *(unsigned short *)__va(BIOS_RAM_SIZE_KB_PTR);
|
|
bios_start <<= 10;
|
|
|
|
/*
|
|
* If bios_start is less than 128K, assume it is bogus
|
|
* and bump it up to 640K. Similarly, if bios_start is above 640K,
|
|
* don't trust it.
|
|
*/
|
|
if (bios_start < BIOS_START_MIN || bios_start > BIOS_START_MAX)
|
|
bios_start = BIOS_START_MAX;
|
|
|
|
/* Get the start address of the EBDA page: */
|
|
ebda_start = get_bios_ebda();
|
|
|
|
/*
|
|
* If the EBDA start address is sane and is below the BIOS region,
|
|
* then also reserve everything from the EBDA start address up to
|
|
* the BIOS region.
|
|
*/
|
|
if (ebda_start >= BIOS_START_MIN && ebda_start < bios_start)
|
|
bios_start = ebda_start;
|
|
|
|
/* Reserve all memory between bios_start and the 1MB mark: */
|
|
memblock_reserve(bios_start, 0x100000 - bios_start);
|
|
}
|