| #include <asm/processor.h> |
| #include "pgtable.h" |
| |
| /* |
| * __force_order is used by special_insns.h asm code to force instruction |
| * serialization. |
| * |
| * It is not referenced from the code, but GCC < 5 with -fPIE would fail |
| * due to an undefined symbol. Define it to make these ancient GCCs work. |
| */ |
| unsigned long __force_order; |
| |
| #define BIOS_START_MIN 0x20000U /* 128K, less than this is insane */ |
| #define BIOS_START_MAX 0x9f000U /* 640K, absolute maximum */ |
| |
| struct paging_config { |
| unsigned long trampoline_start; |
| unsigned long l5_required; |
| }; |
| |
| /* |
| * Trampoline address will be printed by extract_kernel() for debugging |
| * purposes. |
| * |
| * Avoid putting the pointer into .bss as it will be cleared between |
| * paging_prepare() and extract_kernel(). |
| */ |
| unsigned long *trampoline_32bit __section(.data); |
| |
| struct paging_config paging_prepare(void) |
| { |
| struct paging_config paging_config = {}; |
| unsigned long bios_start, ebda_start; |
| |
| /* |
| * Check if LA57 is desired and supported. |
| * |
| * There are two parts to the check: |
| * - if the kernel supports 5-level paging: CONFIG_X86_5LEVEL=y |
| * - if the machine supports 5-level paging: |
| * + CPUID leaf 7 is supported |
| * + the leaf has the feature bit set |
| * |
| * That's substitute for boot_cpu_has() in early boot code. |
| */ |
| if (IS_ENABLED(CONFIG_X86_5LEVEL) && |
| native_cpuid_eax(0) >= 7 && |
| (native_cpuid_ecx(7) & (1 << (X86_FEATURE_LA57 & 31)))) { |
| paging_config.l5_required = 1; |
| } |
| |
| /* |
| * Find a suitable spot for the trampoline. |
| * This code is based on reserve_bios_regions(). |
| */ |
| |
| ebda_start = *(unsigned short *)0x40e << 4; |
| bios_start = *(unsigned short *)0x413 << 10; |
| |
| if (bios_start < BIOS_START_MIN || bios_start > BIOS_START_MAX) |
| bios_start = BIOS_START_MAX; |
| |
| if (ebda_start > BIOS_START_MIN && ebda_start < bios_start) |
| bios_start = ebda_start; |
| |
| /* Place the trampoline just below the end of low memory, aligned to 4k */ |
| paging_config.trampoline_start = bios_start - TRAMPOLINE_32BIT_SIZE; |
| paging_config.trampoline_start = round_down(paging_config.trampoline_start, PAGE_SIZE); |
| |
| trampoline_32bit = (unsigned long *)paging_config.trampoline_start; |
| |
| return paging_config; |
| } |