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paging.c
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paging.c
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/*
* Copyright (C) 2021 Michael Brown <mbrown@fensystems.co.uk>.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
* 02110-1301, USA.
*/
/**
* @file
*
* Paging
*
*/
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>
#include "wimboot.h"
#include "memmap.h"
#include "paging.h"
#if defined(__i386__) || defined(__x86_64__)
/** Virtual address used as a 2MB window during relocation */
#define COPY_WINDOW 0x200000
/** Paging is available */
int paging;
/** Page directory pointer table */
static uint64_t pdpt[4] __attribute__ (( aligned ( PAGE_SIZE ) ));
/** Page directories */
static uint64_t pd[2048] __attribute__ (( aligned ( PAGE_SIZE ) ));
/**
* Check that paging can be supported
*
* @ret supported Paging can be supported on this CPU
*/
static int paging_supported ( void ) {
uint32_t eax;
uint32_t ebx;
uint32_t ecx;
uint32_t edx;
/* Get CPU features */
__asm__ ( "cpuid"
: "=a" ( eax ), "=b" ( ebx ), "=c" ( ecx ), "=d" ( edx )
: "0" ( CPUID_FEATURES ) );
return ( edx & CPUID_FEATURE_EDX_PAE );
}
/**
* Map 2MB page directory entry containing address
*
* @v vaddr Virtual address
* @v paddr Physical address
*/
static void map_page ( uint32_t vaddr, uint64_t paddr ) {
char *byte = ( ( char * ) ( intptr_t ) vaddr );
unsigned int index;
/* Sanity checks */
assert ( ( vaddr & ( PAGE_SIZE_2MB - 1 ) ) == 0 );
assert ( ( paddr & ( PAGE_SIZE_2MB - 1 ) ) == 0 );
/* Populate page directory entry */
index = ( vaddr / PAGE_SIZE_2MB );
pd[index] = ( paddr | PG_P | PG_RW | PG_US | PG_PS );
/* Invalidate TLB */
__asm__ __volatile__ ( "invlpg %0" : : "m" ( *byte ) );
}
/**
* Initialise paging
*
*/
void init_paging ( void ) {
uint32_t addr;
unsigned int i;
/* Do nothing if paging is disabled */
if ( cmdline_linear ) {
DBG ( "Paging disabled\n" );
return;
}
/* Check for PAE */
if ( ! paging_supported() ) {
DBG ( "Paging not possible on this CPU\n" );
return;
}
/* Initialise page directory entries */
addr = 0;
do {
map_page ( addr, addr );
addr += PAGE_SIZE_2MB;
} while ( addr );
/* Initialise page directory pointer table */
for ( i = 0 ; i < ( sizeof ( pdpt ) / sizeof ( pdpt[0] ) ) ; i++ ) {
addr = ( ( intptr_t ) &pd[ i * PAGE_SIZE / sizeof ( pd[0] ) ] );
pdpt[i] = ( addr | PG_P );
}
/* Mark paging as available */
paging = 1;
}
/**
* Enable paging
*
* @v state Saved paging state to fill in
*/
void enable_paging ( struct paging_state *state ) {
unsigned long cr0;
unsigned long cr3;
unsigned long cr4;
/* Do nothing if paging is unavailable */
if ( ! paging )
return;
/* Save paging state */
__asm__ __volatile__ ( "mov %%cr0, %0\n\t"
"mov %%cr3, %1\n\t"
"mov %%cr4, %2\n\t"
: "=r" ( cr0 ), "=r" ( cr3 ), "=r" ( cr4 ) );
state->cr0 = cr0;
state->cr3 = cr3;
state->cr4 = cr4;
/* Disable any existing paging */
__asm__ __volatile__ ( "mov %0, %%cr0" : : "r" ( cr0 & ~CR0_PG ) );
/* Enable PAE */
__asm__ __volatile__ ( "mov %0, %%cr4" : : "r" ( cr4 | CR4_PAE ) );
/* Load page directory pointer table */
__asm__ __volatile__ ( "mov %0, %%cr3" : : "r" ( pdpt ) );
/* Enable paging */
__asm__ __volatile__ ( "mov %0, %%cr0" : : "r" ( cr0 | CR0_PG ) );
}
/**
* Disable paging
*
* @v state Previously saved paging state
*/
void disable_paging ( struct paging_state *state ) {
unsigned long cr0 = state->cr0;
unsigned long cr3 = state->cr3;
unsigned long cr4 = state->cr4;
/* Do nothing if paging is unavailable */
if ( ! paging )
return;
/* Disable paging */
__asm__ __volatile__ ( "mov %0, %%cr0" : : "r" ( cr0 & ~CR0_PG ) );
/* Restore saved paging state */
__asm__ __volatile__ ( "mov %2, %%cr4\n\t"
"mov %1, %%cr3\n\t"
"mov %0, %%cr0\n\t"
: : "r" ( cr0 ), "r" ( cr3 ), "r" ( cr4 ) );
}
/**
* Relocate data out of 32-bit address space, if possible
*
* @v data Start of data
* @v len Length of data
* @ret start Physical start address
*/
uint64_t relocate_memory_high ( void *data, size_t len ) {
intptr_t end = ( ( ( intptr_t ) data ) + len );
struct e820_entry *e820 = NULL;
uint64_t start;
uint64_t dest;
size_t offset;
size_t frag_len;
/* Do nothing if paging is unavailable */
if ( ! paging )
return ( ( intptr_t ) data );
/* Read system memory map */
while ( ( e820 = memmap_next ( e820 ) ) != NULL ) {
/* Find highest compatible placement within this region */
start = ( e820->start + e820->len );
if ( start < ADDR_4GB )
continue;
start = ( ( ( start - end ) & ~( PAGE_SIZE_2MB - 1 ) ) + end );
start -= len;
if ( start < e820->start )
continue;
if ( start < ADDR_4GB )
continue;
/* Relocate to this region */
dest = start;
while ( len ) {
/* Calculate length within this 2MB page */
offset = ( ( ( intptr_t ) data ) &
( PAGE_SIZE_2MB - 1 ) );
frag_len = ( PAGE_SIZE_2MB - offset );
if ( frag_len > len )
frag_len = len;
/* Map copy window to destination */
map_page ( COPY_WINDOW,
( dest & ~( PAGE_SIZE_2MB - 1 ) ) );
/* Copy data through copy window */
memcpy ( ( ( ( void * ) COPY_WINDOW ) + offset ),
data, frag_len );
/* Map original page to destination */
map_page ( ( ( ( intptr_t ) data ) - offset ),
( dest & ~( PAGE_SIZE_2MB - 1 ) ) );
/* Move to next 2MB page */
data += frag_len;
dest += frag_len;
len -= frag_len;
}
/* Remap copy window */
map_page ( COPY_WINDOW, COPY_WINDOW );
return start;
}
/* Leave at original location */
return ( ( intptr_t ) data );
}
#endif /* defined(__i386__) || defined(__x86_64__) */