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/*
* This file sets up page sizes to 1GiB (i.e. huge pages, using only the PML4
* and PDPT, skipping the PDT, and PT).
* We set up identity-page mapping for the 512 GiBs addressable by using static
* PML4 and PDPT tables.
*
* Section 4.5 "4-Level Paging" of Volume 3 of the Intel Software Developer
* Manual guides a lot of the code used in this file.
*/
/*
* Copyright (c) 2018.
* Amaan Cheval <amaan.cheval@gmail.com>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <stdio.h>
#include <assert.h>
#include <bsp.h>
#include <rtems.h>
#include <libcpu/page.h>
#include <rtems/score/cpu.h>
uint64_t amd64_pml4[NUM_PAGE_TABLE_ENTRIES] RTEMS_ALIGNED(4096);
uint64_t amd64_pdpt[NUM_PAGE_TABLE_ENTRIES] RTEMS_ALIGNED(4096);
bool paging_1gib_pages_supported(void)
{
/*
* If CPUID.80000001H:EDX.Page1GB [bit 26] = 1, 1-GByte pages are supported
* with 4-level paging.
*/
uint32_t a, b, c, d;
cpuid(0x80000001, &a, &b, &c, &d);
return (d >> 26) & 1;
}
uint8_t get_maxphysaddr(void)
{
/*
* CPUID.80000008H:EAX[15:8] reports the linear-address width supported by the
* processor. Generally, this value is 48 if CPUID.80000001H:EDX.LM [bit 29] =
* 1 and 32 otherwise.
*/
uint32_t a, b, c, d;
cpuid(0x80000008, &a, &b, &c, &d);
uint8_t maxphysaddr = (a >> 8) & 0xff;
/* This width is referred to as MAXPHYADDR. MAXPHYADDR is at most 52. */
assert(maxphysaddr <= 52);
return maxphysaddr;
}
uint64_t get_mask_for_bits(uint8_t start, uint8_t end)
{
/*
* Create a mask that lets you select bits start:end when logically ANDed with
* a value. For eg.
* get_mask_for_bits(48, 64) = 0xffff000000000000
*/
uint64_t mask = (((uint64_t) 1 << (end - start)) - 1) << start;
return mask;
}
static inline void assert_0s_from_bit(uint64_t entry, uint8_t bit_pos)
{
/* Confirm that bit_pos:64 are all 0s */
assert((entry & get_mask_for_bits(bit_pos, 64)) == 0);
}
uint64_t create_cr3_entry(
uint64_t phys_addr, uint8_t maxphysaddr, uint64_t flags
)
{
/* Confirm PML4 address is aligned on a 4KiB boundary */
assert((phys_addr & 0xfff) == 0);
uint64_t entry = (phys_addr & get_mask_for_bits(12, maxphysaddr)) | flags;
/* Confirm that bits maxphysaddr:64 are 0s */
assert_0s_from_bit(entry, maxphysaddr);
return entry;
}
uint64_t create_pml4_entry(
uint64_t phys_addr, uint8_t maxphysaddr, uint64_t flags
)
{
/* Confirm address we're writing is aligned on a 4KiB boundary */
assert((phys_addr & 0xfff) == 0);
uint64_t entry = (phys_addr & get_mask_for_bits(12, maxphysaddr)) | flags;
/*
* Confirm that bits maxphysaddr:64 are 0s; there are other usable bits there
* such as PAGE_FLAGS_NO_EXECUTE, but we're asserting that those aren't set
* either.
*/
assert_0s_from_bit(entry, maxphysaddr);
return entry;
}
uint64_t create_pdpt_entry(
uint64_t phys_addr, uint8_t maxphysaddr, uint64_t flags
)
{
/* Confirm physical address is a 1GiB aligned page address */
assert((phys_addr & 0x3fffffff) == 0);
uint64_t entry = (phys_addr & get_mask_for_bits(30, maxphysaddr)) | flags;
/*
* Confirm that bits maxphysaddr:64 are 0s; there are other usable bits there
* such as the protection key and PAGE_FLAGS_NO_EXECUTE, but we're asserting
* that those aren't set either.
*/
assert_0s_from_bit(entry, maxphysaddr);
return entry;
}
void paging_init(void)
{
if ( !paging_1gib_pages_supported() ) {
printf("warning: 1 GiB pages aren't supported - trying anyway.\n");
}
const uint8_t maxphysaddr = get_maxphysaddr();
DBG_PRINTF("maxphysaddr = %d\n", maxphysaddr);
const uint64_t gib = (1 << 30);
for (uint32_t i = 0; i < NUM_PAGE_TABLE_ENTRIES; i++) {
amd64_pdpt[i] = create_pdpt_entry(
/* This is the i-th GiB for identity-mapping */
(uint64_t) i * gib,
maxphysaddr,
/* Setting huge page in the PDPTE gives us 1 GiB pages */
PAGE_FLAGS_DEFAULTS | PAGE_FLAGS_HUGE_PAGE
);
amd64_pml4[i] = create_pml4_entry(
(uint64_t) amd64_pdpt,
maxphysaddr,
PAGE_FLAGS_DEFAULTS
);
}
amd64_set_cr3(
create_cr3_entry(
(uint64_t) &amd64_pml4,
maxphysaddr,
PAGE_FLAGS_WRITE_THROUGH
)
);
}
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