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#include <asm/processor.h>
#include "pgtable.h"
#include "../string.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;
};
/* Buffer to preserve trampoline memory */
static char trampoline_save[TRAMPOLINE_32BIT_SIZE];
/*
* The page table is going to be used instead of page table in the trampoline
* memory.
*
* It must not be in BSS as BSS is cleared after cleanup_trampoline().
*/
static char top_pgtable[PAGE_SIZE] __aligned(PAGE_SIZE) __section(.data);
/*
* 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;
/* Preserve trampoline memory */
memcpy(trampoline_save, trampoline_32bit, TRAMPOLINE_32BIT_SIZE);
/* Clear trampoline memory first */
memset(trampoline_32bit, 0, TRAMPOLINE_32BIT_SIZE);
/* Copy trampoline code in place */
memcpy(trampoline_32bit + TRAMPOLINE_32BIT_CODE_OFFSET / sizeof(unsigned long),
&trampoline_32bit_src, TRAMPOLINE_32BIT_CODE_SIZE);
/*
* The code below prepares page table in trampoline memory.
*
* The new page table will be used by trampoline code for switching
* from 4- to 5-level paging or vice versa.
*
* If switching is not required, the page table is unused: trampoline
* code wouldn't touch CR3.
*/
/*
* We are not going to use the page table in trampoline memory if we
* are already in the desired paging mode.
*/
if (paging_config.l5_required == !!(native_read_cr4() & X86_CR4_LA57))
goto out;
if (paging_config.l5_required) {
/*
* For 4- to 5-level paging transition, set up current CR3 as
* the first and the only entry in a new top-level page table.
*/
trampoline_32bit[TRAMPOLINE_32BIT_PGTABLE_OFFSET] = __native_read_cr3() | _PAGE_TABLE_NOENC;
} else {
unsigned long src;
/*
* For 5- to 4-level paging transition, copy page table pointed
* by first entry in the current top-level page table as our
* new top-level page table.
*
* We cannot just point to the page table from trampoline as it
* may be above 4G.
*/
src = *(unsigned long *)__native_read_cr3() & PAGE_MASK;
memcpy(trampoline_32bit + TRAMPOLINE_32BIT_PGTABLE_OFFSET / sizeof(unsigned long),
(void *)src, PAGE_SIZE);
}
out:
return paging_config;
}
void cleanup_trampoline(void)
{
void *trampoline_pgtable;
trampoline_pgtable = trampoline_32bit + TRAMPOLINE_32BIT_PGTABLE_OFFSET;
/*
* Move the top level page table out of trampoline memory,
* if it's there.
*/
if ((void *)__native_read_cr3() == trampoline_pgtable) {
memcpy(top_pgtable, trampoline_pgtable, PAGE_SIZE);
native_write_cr3((unsigned long)top_pgtable);
}
/* Restore trampoline memory */
memcpy(trampoline_32bit, trampoline_save, TRAMPOLINE_32BIT_SIZE);
}
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