forked from AbleOS/holey-bytes
329 lines
9.3 KiB
Rust
329 lines
9.3 KiB
Rust
mod paging;
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use self::paging::{PageTable, Permission, PtEntry};
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use super::trap::HandleTrap;
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use alloc::boxed::Box;
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use derive_more::Display;
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/// HoleyBytes virtual memory
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#[derive(Clone, Debug)]
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pub struct Memory {
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/// Root page table
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root_pt: *mut PageTable,
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}
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impl Default for Memory {
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fn default() -> Self {
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Self {
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root_pt: Box::into_raw(Box::default()),
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}
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}
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}
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impl Drop for Memory {
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fn drop(&mut self) {
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let _ = unsafe { Box::from_raw(self.root_pt) };
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}
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}
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impl Memory {
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// HACK: Just for allocation testing, will be removed when proper memory interfaces
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// implemented.
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pub fn insert_test_page(&mut self) {
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unsafe {
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let mut entry = PtEntry::new(
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{
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let layout = alloc::alloc::Layout::from_size_align_unchecked(4096, 4096);
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let ptr = alloc::alloc::alloc_zeroed(layout);
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if ptr.is_null() {
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alloc::alloc::handle_alloc_error(layout);
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}
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core::ptr::write_bytes(ptr, 69, 10);
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ptr.cast()
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},
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Permission::Write,
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);
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for _ in 0..4 {
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let mut pt = Box::<PageTable>::default();
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pt[0] = entry;
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entry = PtEntry::new(Box::into_raw(pt) as _, Permission::Node);
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}
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(*self.root_pt)[0] = entry;
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}
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}
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/// Load value from an address
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///
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/// # Safety
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/// Applies same conditions as for [`core::ptr::copy_nonoverlapping`]
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pub unsafe fn load(
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&mut self,
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addr: u64,
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target: *mut u8,
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count: usize,
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traph: &mut impl HandleTrap,
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) -> Result<(), LoadError> {
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self.memory_access(
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addr,
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target,
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count,
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|perm| {
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matches!(
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perm,
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Permission::Readonly | Permission::Write | Permission::Exec
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)
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},
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|src, dst, count| core::ptr::copy_nonoverlapping(src, dst, count),
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traph,
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)
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.map_err(|_| LoadError)
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}
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/// Store value to an address
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///
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/// # Safety
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/// Applies same conditions as for [`core::ptr::copy_nonoverlapping`]
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pub unsafe fn store(
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&mut self,
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addr: u64,
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source: *const u8,
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count: usize,
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traph: &mut impl HandleTrap,
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) -> Result<(), StoreError> {
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self.memory_access(
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addr,
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source.cast_mut(),
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count,
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|perm| perm == Permission::Write,
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|dst, src, count| core::ptr::copy_nonoverlapping(src, dst, count),
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traph,
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)
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.map_err(|_| StoreError)
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}
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/// Copy a block of memory
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pub unsafe fn block_copy(&mut self, src: u64, dst: u64, count: u64) -> Result<(), ()> {
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/* let count = usize::try_from(count).expect("?conradluget a better CPU");
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let mut srcs = PageSplitter::new(src, count, self.root_pt);
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let mut dsts = PageSplitter::new(dst, count, self.root_pt);
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let mut c_src = srcs.next().ok_or(())?;
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let mut c_dst = dsts.next().ok_or(())?;
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loop {
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let min_size = c_src.size.min(c_dst.size);
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unsafe {
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core::ptr::copy(c_src.ptr, c_dst.ptr, min_size);
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}
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match (
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match c_src.size.saturating_sub(min_size) {
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0 => srcs.next(),
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size => Some(PageSplitResult { size, ..c_src }),
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},
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match c_dst.size.saturating_sub(min_size) {
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0 => dsts.next(),
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size => Some(PageSplitResult { size, ..c_dst }),
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},
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) {
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(None, None) => return Ok(()),
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(Some(src), Some(dst)) => (c_src, c_dst) = (src, dst),
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_ => return Err(()),
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}
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} */
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// TODO
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Err(())
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}
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/// Split address to pages, check their permissions and feed pointers with offset
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/// to a specified function.
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///
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/// If page is not found, execute page fault trap handler.
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fn memory_access(
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&mut self,
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src: u64,
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mut dst: *mut u8,
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len: usize,
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permission_check: fn(Permission) -> bool,
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action: fn(*mut u8, *mut u8, usize),
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traph: &mut impl HandleTrap,
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) -> Result<(), ()> {
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let mut pspl = AddrSplitter::new(src, len, self.root_pt);
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loop {
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match pspl.next() {
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// Page found
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Some(Ok(AddrSplitOk { ptr, size, perm })) => {
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if !permission_check(perm) {
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return Err(());
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}
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// Perform memory action and bump dst pointer
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action(ptr, dst, size);
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dst = unsafe { dst.add(size) };
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}
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Some(Err(AddrSplitError { addr, size })) => {
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// Execute page fault handler
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if traph.page_fault(self, addr, size, dst) {
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// Shift the splitter address
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pspl.bump(size);
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// Bump dst pointer
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dst = unsafe { dst.add(size as _) };
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} else {
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return Err(()); // Unhandleable
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}
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}
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None => return Ok(()),
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}
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}
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}
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}
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/// Result from address split
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struct AddrSplitOk {
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/// Pointer to the start for perform operation
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ptr: *mut u8,
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/// Size to the end of page / end of desired size
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size: usize,
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/// Page permission
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perm: Permission,
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}
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struct AddrSplitError {
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/// Address of failure
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addr: u64,
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/// Requested page size
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size: PageSize,
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}
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/// Address splitter into pages
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struct AddrSplitter {
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/// Current address
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addr: u64,
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/// Size left
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size: usize,
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/// Page table
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pagetable: *const PageTable,
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}
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impl AddrSplitter {
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/// Create a new page splitter
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pub const fn new(addr: u64, size: usize, pagetable: *const PageTable) -> Self {
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Self {
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addr,
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size,
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pagetable,
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}
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}
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/// Bump address by size X
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fn bump(&mut self, page_size: PageSize) {
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self.addr += page_size as u64;
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self.size = self.size.saturating_sub(page_size as _);
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}
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}
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impl Iterator for AddrSplitter {
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type Item = Result<AddrSplitOk, AddrSplitError>;
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fn next(&mut self) -> Option<Self::Item> {
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// The end, everything is fine
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if self.size == 0 {
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return None;
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}
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let (base, perm, size, offset) = 'a: {
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let mut current_pt = self.pagetable;
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// Walk the page table
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for lvl in (0..5).rev() {
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// Get an entry
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unsafe {
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let entry = (*current_pt).get_unchecked(
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usize::try_from((self.addr >> (lvl * 9 + 12)) & ((1 << 9) - 1))
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.expect("?conradluget a better CPU"),
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);
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let ptr = entry.ptr();
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match entry.permission() {
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// No page → page fault
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Permission::Empty => {
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return Some(Err(AddrSplitError {
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addr: self.addr,
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size: PageSize::from_lvl(lvl)?,
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}))
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}
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// Node → proceed waking
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Permission::Node => current_pt = ptr as _,
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// Leaft → return relevant data
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perm => {
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break 'a (
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// Pointer in host memory
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ptr as *mut u8,
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perm,
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PageSize::from_lvl(lvl)?,
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// In-page offset
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self.addr as usize & ((1 << (lvl * 9 + 12)) - 1),
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);
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}
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}
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}
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}
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return None; // Reached the end (should not happen)
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};
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// Get available byte count in the selected page with offset
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let avail = (size as usize - offset).clamp(0, self.size);
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self.bump(size);
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Some(Ok(AddrSplitOk {
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ptr: unsafe { base.add(offset) }, // Return pointer to the start of region
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size: avail,
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perm,
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}))
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}
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}
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/// Page size
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#[derive(Clone, Copy, Debug, PartialEq, Eq)]
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pub enum PageSize {
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/// 4 KiB page (on level 0)
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Size4K = 4096,
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/// 2 MiB page (on level 1)
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Size2M = 1024 * 1024 * 2,
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/// 1 GiB page (on level 2)
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Size1G = 1024 * 1024 * 1024,
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}
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impl PageSize {
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/// Convert page table level to size of page
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fn from_lvl(lvl: u8) -> Option<Self> {
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match lvl {
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0 => Some(PageSize::Size4K),
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1 => Some(PageSize::Size2M),
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2 => Some(PageSize::Size1G),
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_ => None,
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}
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}
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}
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/// Unhandled load access trap
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#[derive(Clone, Copy, Display, Debug, PartialEq, Eq)]
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pub struct LoadError;
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/// Unhandled store access trap
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#[derive(Clone, Copy, Display, Debug, PartialEq, Eq)]
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pub struct StoreError;
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