Skip to content

Commit 9095737

Browse files
Andy-Python-ProgrammerAndy-Python-Programmer
committed
feat(fork): only copy necessary mappings
Do not copy page table entries that can be mapped correctly on-demand when a page fault occurs. Signed-off-by: Anhad Singh <andypythonappdeveloper@gmail.com>
1 parent 15ca628 commit 9095737

File tree

8 files changed

+256
-282
lines changed

8 files changed

+256
-282
lines changed

‎src/aero_kernel/src/arch/x86_64/task.rs‎

Lines changed: 3 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -313,11 +313,9 @@ impl ArchTask {
313313
})
314314
}
315315

316-
pub fn fork(&self) -> Result<Self, MapToError<Size4KiB>> {
316+
pub fn fork(&self, address_space: AddressSpace) -> Result<Self, MapToError<Size4KiB>> {
317317
assert!(self.user, "cannot fork a kernel task");
318318

319-
let new_address_space = AddressSpace::this().offset_page_table().fork()?;
320-
321319
// Since the fork function marks all of the userspace entries in both the forked
322320
// and the parent address spaces as read only, we will flush the page table of the
323321
// current process to trigger COW.
@@ -346,14 +344,14 @@ impl ArchTask {
346344

347345
*context = Context::default();
348346
context.rip = fork_init as u64;
349-
context.cr3 = new_address_space.cr3().start_address().as_u64();
347+
context.cr3 = address_space.cr3().start_address().as_u64();
350348

351349
let fpu_storage = self.fpu_storage.unwrap().clone();
352350

353351
Ok(Self {
354352
context: unsafe { Unique::new_unchecked(context) },
355353
context_switch_rsp: VirtAddr::new(switch_stack as u64),
356-
address_space: new_address_space,
354+
address_space,
357355
user: true,
358356

359357
// The FS and GS bases are inherited from the parent process.

‎src/aero_kernel/src/fs/file_table.rs‎

Lines changed: 12 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -57,6 +57,18 @@ impl FileHandle {
5757
}
5858
}
5959

60+
#[inline]
61+
pub fn is_writable(&self) -> bool {
62+
self.flags()
63+
.intersects(OpenFlags::O_WRONLY | OpenFlags::O_RDWR)
64+
}
65+
66+
#[inline]
67+
pub fn is_readable(&self) -> bool {
68+
self.flags()
69+
.intersects(OpenFlags::O_RDONLY | OpenFlags::O_RDWR)
70+
}
71+
6072
pub fn flags(&self) -> OpenFlags {
6173
*self.flags.read()
6274
}

‎src/aero_kernel/src/fs/procfs.rs‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -200,7 +200,7 @@ impl INodeInterface for LockedProcINode {
200200
"start": map.start_addr.as_u64(),
201201
"end": map.end_addr.as_u64(),
202202
"flags": map.flags.bits(),
203-
"protection": map.protection.bits(),
203+
"protection": map.protection().bits(),
204204
}));
205205
});
206206

‎src/aero_kernel/src/main.rs‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -50,7 +50,8 @@
5050
associated_type_defaults,
5151
trait_upcasting,
5252
asm_const,
53-
sync_unsafe_cell
53+
sync_unsafe_cell,
54+
// effects
5455
)]
5556
// TODO(andypython): can we remove the dependency of "prelude_import" and "lang_items"?
5657
// `lang_items` => is currently used for the personality function (`rust_eh_personality`).

‎src/aero_kernel/src/mem/paging/mapper.rs‎

Lines changed: 42 additions & 178 deletions
Original file line numberDiff line numberDiff line change
@@ -18,9 +18,7 @@
1818
// Some code borrowed from the x86_64 crate (MIT + Apache) and add support for 5-level paging
1919
// and some kernel specific features that cannot be directly done in the crate itself.
2020

21-
use core::ops::Range;
22-
23-
use crate::mem::AddressSpace;
21+
use core::ops::{Range, RangeInclusive};
2422

2523
use super::addr::{PhysAddr, VirtAddr};
2624
use super::page::{AddressNotAligned, Page, PageSize, PhysFrame, Size1GiB, Size2MiB, Size4KiB};
@@ -1139,187 +1137,53 @@ impl<'a> OffsetPageTable<'a> {
11391137
Ok(())
11401138
}
11411139

1142-
pub fn fork(&mut self) -> Result<AddressSpace, MapToError<Size4KiB>> {
1143-
let mut address_space = AddressSpace::new()?; // Allocate the new address space
1144-
1145-
let offset_table = address_space.offset_page_table();
1146-
let make_next_level = |table: &mut PageTable,
1147-
i: usize|
1148-
-> Result<(bool, &mut PageTable), MapToError<Size4KiB>> {
1149-
let entry = &mut table[i];
1150-
let created = if !entry.flags().contains(PageTableFlags::PRESENT) {
1151-
let frame = FRAME_ALLOCATOR
1152-
.allocate_frame()
1153-
.ok_or(MapToError::FrameAllocationFailed)?;
1154-
1155-
entry.set_frame(
1156-
frame,
1157-
PageTableFlags::PRESENT
1158-
| PageTableFlags::WRITABLE
1159-
| PageTableFlags::USER_ACCESSIBLE,
1160-
);
1161-
1162-
true
1163-
} else {
1164-
entry.set_flags(
1165-
PageTableFlags::PRESENT
1166-
| PageTableFlags::WRITABLE
1167-
| PageTableFlags::USER_ACCESSIBLE,
1168-
);
1169-
1170-
false
1171-
};
1172-
1173-
let page_table_ptr = {
1174-
let addr = entry.frame().unwrap().start_address().as_hhdm_virt();
1175-
addr.as_mut_ptr::<PageTable>()
1176-
};
1177-
1178-
let page_table: &mut PageTable = unsafe { &mut *page_table_ptr };
1179-
if created {
1180-
page_table.zero();
1140+
pub fn copy_page_range(&mut self, src: &mut OffsetPageTable, range: RangeInclusive<VirtAddr>) {
1141+
let mut map_to = |src: &mut OffsetPageTable, addr, frame, flags| match frame {
1142+
MappedFrame::Size4KiB(frame) => {
1143+
let page = Page::<Size4KiB>::containing_address(addr);
1144+
1145+
unsafe {
1146+
self.map_to_with_table_flags(
1147+
page,
1148+
frame,
1149+
flags,
1150+
PageTableFlags::PRESENT
1151+
| PageTableFlags::USER_ACCESSIBLE
1152+
| PageTableFlags::WRITABLE,
1153+
)
1154+
}
1155+
.unwrap()
1156+
// operating on an inactive page table
1157+
.ignore();
1158+
1159+
unsafe { src.update_flags(page, flags) }
1160+
.unwrap()
1161+
// caller is required to invalidate the TLB
1162+
.ignore();
11811163
}
1182-
1183-
Ok((created, page_table))
1164+
_ => todo!(),
11841165
};
11851166

1186-
let last_level_fork = |entry: &mut PageTableEntry, n1: &mut PageTable, i: usize| {
1187-
let mut flags = entry.flags();
1167+
let mut addr = *range.start();
11881168

1189-
// Check if the mapping is shared.
1190-
// if !flags.contains(PageTableFlags::BIT_10) {
1191-
// Setup copy on write page.
1192-
flags.remove(PageTableFlags::WRITABLE);
1193-
// }
1169+
while addr != *range.end() {
1170+
match src.translate(addr) {
1171+
TranslateResult::Mapped {
1172+
frame,
1173+
offset,
1174+
flags,
1175+
} => {
1176+
assert_eq!(offset, 0, "unaligned page range");
1177+
map_to(src, addr, frame, flags & !PageTableFlags::WRITABLE);
1178+
}
11941179

1195-
entry.set_flags(flags);
1196-
n1[i].set_frame(entry.frame().unwrap(), flags);
1197-
};
1180+
TranslateResult::NotMapped => {}
1181+
TranslateResult::InvalidFrameAddress(addr) => {
1182+
panic!("invalid frame address {:#x}", addr);
1183+
}
1184+
}
11981185

1199-
// We loop through each of the page table entries in the page table which are user
1200-
// accessible and we remove the writeable flag from the entry if present. This will
1201-
// make the page table entry copy on the first write. Then we clone the page table entry
1202-
// and place it in the new page table.
1203-
if self.inner.level_5_paging_enabled {
1204-
self.inner.page_table.for_entries_mut(
1205-
PageTableFlags::PRESENT | PageTableFlags::USER_ACCESSIBLE,
1206-
|i, _, table| {
1207-
let (_, n4) = make_next_level(offset_table.inner.page_table, i)?;
1208-
let mut count_4 = 0;
1209-
1210-
table.for_entries_mut(
1211-
PageTableFlags::PRESENT | PageTableFlags::USER_ACCESSIBLE,
1212-
|j, _, table| {
1213-
let (w3, n3) = make_next_level(n4, j)?;
1214-
let mut count_3 = 0;
1215-
1216-
if w3 {
1217-
count_4 += 1;
1218-
}
1219-
1220-
table.for_entries_mut(
1221-
PageTableFlags::PRESENT | PageTableFlags::USER_ACCESSIBLE,
1222-
|k, _, table| {
1223-
let (w2, n2) = make_next_level(n3, k)?;
1224-
let mut count_2 = 0;
1225-
1226-
if w2 {
1227-
count_3 += 1;
1228-
}
1229-
1230-
table.for_entries_mut(
1231-
PageTableFlags::PRESENT | PageTableFlags::USER_ACCESSIBLE,
1232-
|l, _, table| {
1233-
let (w1, n1) = make_next_level(n2, l)?;
1234-
let mut count_1 = 0;
1235-
1236-
if w1 {
1237-
count_2 += 1;
1238-
}
1239-
1240-
table.for_entries_mut(
1241-
PageTableFlags::PRESENT
1242-
| PageTableFlags::USER_ACCESSIBLE,
1243-
|i, entry, _| {
1244-
last_level_fork(entry, n1, i);
1245-
1246-
count_1 += 1;
1247-
Ok(())
1248-
},
1249-
)?;
1250-
1251-
n2[l].set_entry_count(count_1);
1252-
Ok(())
1253-
},
1254-
)?;
1255-
1256-
n3[k].set_entry_count(count_2);
1257-
Ok(())
1258-
},
1259-
)?;
1260-
1261-
n4[j].set_entry_count(count_3);
1262-
Ok(())
1263-
},
1264-
)?;
1265-
1266-
offset_table.inner.page_table[i].set_entry_count(count_4);
1267-
Ok(())
1268-
},
1269-
)?;
1270-
} else {
1271-
self.inner.page_table.for_entries_mut(
1272-
PageTableFlags::PRESENT | PageTableFlags::USER_ACCESSIBLE,
1273-
|i, _, table| {
1274-
let (_, n3) = make_next_level(offset_table.inner.page_table, i)?;
1275-
let mut count_3 = 0;
1276-
1277-
table.for_entries_mut(
1278-
PageTableFlags::PRESENT | PageTableFlags::USER_ACCESSIBLE,
1279-
|k, _, table| {
1280-
let (w2, n2) = make_next_level(n3, k)?;
1281-
let mut count_2 = 0;
1282-
1283-
if w2 {
1284-
count_3 += 1;
1285-
}
1286-
1287-
table.for_entries_mut(
1288-
PageTableFlags::PRESENT | PageTableFlags::USER_ACCESSIBLE,
1289-
|l, _, table| {
1290-
let (w1, n1) = make_next_level(n2, l)?;
1291-
let mut count_1 = 0;
1292-
1293-
if w1 {
1294-
count_2 += 1;
1295-
}
1296-
1297-
table.for_entries_mut(
1298-
PageTableFlags::PRESENT | PageTableFlags::USER_ACCESSIBLE,
1299-
|i, entry, _| {
1300-
last_level_fork(entry, n1, i);
1301-
1302-
count_1 += 1;
1303-
Ok(())
1304-
},
1305-
)?;
1306-
1307-
n2[l].set_entry_count(count_1);
1308-
Ok(())
1309-
},
1310-
)?;
1311-
1312-
n3[k].set_entry_count(count_2);
1313-
Ok(())
1314-
},
1315-
)?;
1316-
1317-
offset_table.inner.page_table[i].set_entry_count(count_3);
1318-
Ok(())
1319-
},
1320-
)?;
1186+
addr += Size4KiB::SIZE;
13211187
}
1322-
1323-
Ok(address_space)
13241188
}
13251189
}

‎src/aero_kernel/src/syscall/process.rs‎

Lines changed: 1 addition & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -181,8 +181,7 @@ pub fn mmap(
181181
.current_task()
182182
.file_table
183183
.get_handle(fd)
184-
.ok_or(SyscallError::EBADF)?
185-
.dirnode(),
184+
.ok_or(SyscallError::EBADF)?,
186185
);
187186
}
188187

0 commit comments

Comments
 (0)