1 #include <linux/kernel.h> 2 #include <linux/init.h> 3 #include <linux/memblock.h> 4 5 #include <asm/setup.h> 6 #include <asm/bios_ebda.h> 7 8 /* 9 * The BIOS places the EBDA/XBDA at the top of conventional 10 * memory, and usually decreases the reported amount of 11 * conventional memory (int 0x12) too. This also contains a 12 * workaround for Dell systems that neglect to reserve EBDA. 13 * The same workaround also avoids a problem with the AMD768MPX 14 * chipset: reserve a page before VGA to prevent PCI prefetch 15 * into it (errata #56). Usually the page is reserved anyways, 16 * unless you have no PS/2 mouse plugged in. 17 * 18 * This functions is deliberately very conservative. Losing 19 * memory in the bottom megabyte is rarely a problem, as long 20 * as we have enough memory to install the trampoline. Using 21 * memory that is in use by the BIOS or by some DMA device 22 * the BIOS didn't shut down *is* a big problem. 23 */ 24 25 #define BIOS_LOWMEM_KILOBYTES 0x413 26 #define LOWMEM_CAP 0x9f000U /* Absolute maximum */ 27 #define INSANE_CUTOFF 0x20000U /* Less than this = insane */ 28 29 void __init reserve_ebda_region(void) 30 { 31 unsigned int lowmem, ebda_addr; 32 33 /* 34 * To determine the position of the EBDA and the 35 * end of conventional memory, we need to look at 36 * the BIOS data area. In a paravirtual environment 37 * that area is absent. We'll just have to assume 38 * that the paravirt case can handle memory setup 39 * correctly, without our help. 40 */ 41 if (!x86_platform.legacy.ebda_search) 42 return; 43 44 /* end of low (conventional) memory */ 45 lowmem = *(unsigned short *)__va(BIOS_LOWMEM_KILOBYTES); 46 lowmem <<= 10; 47 48 /* start of EBDA area */ 49 ebda_addr = get_bios_ebda(); 50 51 /* 52 * Note: some old Dells seem to need 4k EBDA without 53 * reporting so, so just consider the memory above 0x9f000 54 * to be off limits (bugzilla 2990). 55 */ 56 57 /* If the EBDA address is below 128K, assume it is bogus */ 58 if (ebda_addr < INSANE_CUTOFF) 59 ebda_addr = LOWMEM_CAP; 60 61 /* If lowmem is less than 128K, assume it is bogus */ 62 if (lowmem < INSANE_CUTOFF) 63 lowmem = LOWMEM_CAP; 64 65 /* Use the lower of the lowmem and EBDA markers as the cutoff */ 66 lowmem = min(lowmem, ebda_addr); 67 lowmem = min(lowmem, LOWMEM_CAP); /* Absolute cap */ 68 69 /* reserve all memory between lowmem and the 1MB mark */ 70 memblock_reserve(lowmem, 0x100000 - lowmem); 71 } 72