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fix: Level 3 translation fault

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This commit is contained in:
Alexander Neuhäuser
2026-03-15 12:27:36 +01:00
parent e84ce6ab91
commit 95a5037b91
2 changed files with 99 additions and 40 deletions
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100
src/aarch64/mmu.rs
View File

@@ -11,6 +11,7 @@ unsafe extern "C" {
const BLOCK: u64 = 0b01;
const TABLE: u64 = 0b11;
const PAGE: u64 = 0b11;
pub const EL0_ACCESSIBLE: u64 = 1 << 6;
@@ -91,6 +92,7 @@ pub fn allocate_memory(
Ok(())
}
pub fn allocate_memory_explicit(
mut virtual_address: usize,
mut size: usize,
@@ -103,9 +105,9 @@ pub fn allocate_memory_explicit(
let level1_blocks = size / LEVEL1_BLOCK_SIZE;
size %= LEVEL1_BLOCK_SIZE;
let level2_blocks = size / LEVEL2_BLOCK_SIZE;
let mut level2_blocks = size / LEVEL2_BLOCK_SIZE;
size %= LEVEL2_BLOCK_SIZE;
let level3_pages = size / GRANULARITY;
let mut level3_pages = size / GRANULARITY;
if size % GRANULARITY != 0 {
return Err(NovaError::InvalidGranularity);
}
@@ -114,6 +116,31 @@ pub fn allocate_memory_explicit(
todo!("Currently not supported");
}
let l2_alignment = (physical_address % LEVEL2_BLOCK_SIZE) / GRANULARITY;
if l2_alignment != 0 {
let l3_diff = LEVEL2_BLOCK_SIZE / GRANULARITY - l2_alignment;
if l3_diff > level3_pages {
level2_blocks -= 1;
level3_pages += TABLE_ENTRY_COUNT;
}
level3_pages -= l3_diff;
for _ in 0..l3_diff {
unsafe {
alloc_page_explicit(
virtual_address,
physical_address,
&mut TRANSLATIONTABLE_TTBR0,
additional_flags,
)?;
}
virtual_address += GRANULARITY;
physical_address += GRANULARITY;
}
}
for _ in 0..level2_blocks {
unsafe {
alloc_block_l2_explicit(
@@ -178,13 +205,15 @@ fn map_page(
) -> Result<(), NovaError> {
let (l1_off, l2_off, l3_off) = virtual_address_to_table_offset(virtual_address);
let table = navigate_table(base_table, [l1_off, l2_off, 0], 2)?;
let offsets = [l1_off, l2_off];
let table = navigate_table(base_table, &offsets)?;
if table.0[l3_off] & 0b11 > 0 {
return Err(NovaError::Paging);
}
table.0[l3_off] = create_block_descriptor_entry(physical_address, additional_flags);
table.0[l3_off] = create_page_descriptor_entry(physical_address, additional_flags);
Ok(())
}
@@ -203,6 +232,10 @@ pub fn alloc_block_l2_explicit(
base_table: &mut PageTable,
additional_flags: u64,
) -> Result<(), NovaError> {
if physical_address % LEVEL2_BLOCK_SIZE != 0 {
return Err(NovaError::Misalignment);
}
reserve_block_explicit(physical_address)?;
map_l2_block(virtual_addr, physical_address, base_table, additional_flags)
}
@@ -214,8 +247,8 @@ pub fn map_l2_block(
additional_flags: u64,
) -> Result<(), NovaError> {
let (l1_off, l2_off, _) = virtual_address_to_table_offset(virtual_addr);
let table = navigate_table(base_table, [l1_off, 0, 0], 1)?;
let offsets = [l1_off];
let table = navigate_table(base_table, &offsets)?;
// Verify virtual address is available.
if table.0[l2_off] & 0b11 != 0 {
@@ -312,13 +345,21 @@ fn reserve_block_explicit(physical_address: usize) -> Result<(), NovaError> {
}
fn create_block_descriptor_entry(physical_address: usize, additional_flags: u64) -> u64 {
(physical_address as u64 & 0x0000_FFFF_FFE0_0000)
(physical_address as u64 & 0x0000_FFFF_FFFF_F000)
| BLOCK
| ACCESS_FLAG
| INNER_SHAREABILITY
| additional_flags
}
fn create_page_descriptor_entry(physical_address: usize, additional_flags: u64) -> u64 {
(physical_address as u64 & 0x0000_FFFF_FFFF_F000)
| PAGE
| ACCESS_FLAG
| INNER_SHAREABILITY
| additional_flags
}
fn create_table_descriptor_entry(addr: usize) -> u64 {
0 | (addr as u64 & 0x0000_FFFF_FFFF_F000) | TABLE
}
@@ -331,22 +372,38 @@ fn virtual_address_to_table_offset(virtual_addr: usize) -> (usize, usize, usize)
(l1_off, l2_off, l3_off)
}
fn navigate_table(
initial_table: &mut PageTable,
offsets: [usize; 3],
offsets_size: usize,
) -> Result<&mut PageTable, NovaError> {
pub fn sim_l3_access(addr: usize) {
unsafe {
let entry1 = TRANSLATIONTABLE_TTBR0.0[addr / LEVEL1_BLOCK_SIZE];
let table2 = &mut *(get_table_entry_address(entry1) as *mut PageTable);
let entry2 = table2.0[(addr % LEVEL1_BLOCK_SIZE) / LEVEL2_BLOCK_SIZE];
let table3 = &mut *(get_table_entry_address(entry2) as *mut PageTable);
let entry3 = table3.0[(addr % LEVEL2_BLOCK_SIZE) / GRANULARITY];
}
}
fn navigate_table<'a>(
initial_table: &'a mut PageTable,
offsets: &'a [usize],
) -> Result<&'a mut PageTable, NovaError> {
let root_table_ptr = initial_table as *mut PageTable;
let mut table = initial_table;
for i in 0..offsets_size {
let offset = offsets[i];
for offset in offsets {
table = next_table(table, *offset, root_table_ptr)?;
}
Ok(table)
}
fn next_table(
table: &mut PageTable,
offset: usize,
root_table_ptr: *mut PageTable,
) -> Result<&mut PageTable, NovaError> {
match table.0[offset] & 0b11 {
0 => {
let new_table_addr = reserve_page();
table.0[offset] = create_table_descriptor_entry(new_table_addr);
table =
unsafe { &mut *(get_table_entry_address(table.0[offset]) as *mut PageTable) };
map_page(
new_table_addr,
@@ -354,16 +411,13 @@ fn navigate_table(
unsafe { &mut *root_table_ptr },
NORMAL_MEM | WRITABLE | PXN | UXN,
)?;
Ok(unsafe { &mut *(get_table_entry_address(table.0[offset]) as *mut PageTable) })
}
1 => return Err(NovaError::Paging),
3 => {
table =
unsafe { &mut *(get_table_entry_address(table.0[offset]) as *mut PageTable) }
3 => Ok(unsafe { &mut *(get_table_entry_address(table.0[offset]) as *mut PageTable) }),
_ => unreachable!(),
}
_ => panic!(),
};
}
Ok(table)
}
fn find_unallocated_page() -> Option<usize> {

13
src/main.rs
View File

@@ -13,8 +13,8 @@ extern crate alloc;
use nova::{
aarch64::{
mmu::{
allocate_memory_explicit, EL0_ACCESSIBLE, LEVEL2_BLOCK_SIZE, NORMAL_MEM, PXN, UXN,
WRITABLE,
allocate_memory_explicit, sim_l3_access, EL0_ACCESSIBLE, NORMAL_MEM,
PXN, UXN, WRITABLE,
},
registers::{daif, read_id_aa64mmfr0_el1},
},
@@ -77,11 +77,12 @@ pub extern "C" fn main() -> ! {
// TODO: Investigate why the size is off
allocate_memory_explicit(
0x3c100000,
1080 * 1920 * 4 + LEVEL2_BLOCK_SIZE + LEVEL2_BLOCK_SIZE,
1080 * 1920 * 4,
0x3c100000,
NORMAL_MEM | PXN | UXN | WRITABLE | EL0_ACCESSIBLE,
)
.unwrap();
sim_l3_access(0x3c100000);
configure_mmu_el1();
};
@@ -108,7 +109,11 @@ pub extern "C" fn kernel_main() -> ! {
nova::initialize_kernel();
println!("Exception Level: {}", get_current_el());
daif::unmask_all();
let fb = FrameBuffer::default();
for i in 0..1080 {
fb.draw_pixel(50, i, RED);
}
unsafe {
el1_to_el0();
};
@@ -131,7 +136,7 @@ pub extern "C" fn el0() -> ! {
let fb = FrameBuffer::default();
for i in 0..1080 {
for i in 600..1080 {
fb.draw_pixel(50, i, RED);
}
fb.draw_square(500, 500, 600, 700, RED);