1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
use crate::structures::paging::{
    frame::PhysFrame,
    frame_alloc::FrameAllocator,
    mapper::*,
    page::{Page, Size1GiB, Size2MiB, Size4KiB},
    page_table::{FrameError, PageTable, PageTableEntry, PageTableFlags},
};

/// A Mapper implementation that relies on a PhysAddr to VirtAddr conversion function.
///
/// This type requires that the all physical page table frames are mapped to some virtual
/// address. Normally, this is done by mapping the complete physical address space into
/// the virtual address space at some offset. Other mappings between physical and virtual
/// memory are possible too, as long as they can be calculated as an `PhysAddr` to
/// `VirtAddr` closure.
#[derive(Debug)]
pub struct MappedPageTable<'a, P: PhysToVirt> {
    page_table_walker: PageTableWalker<P>,
    level_4_table: &'a mut PageTable,
}

impl<'a, P: PhysToVirt> MappedPageTable<'a, P> {
    /// Creates a new `MappedPageTable` that uses the passed closure for converting virtual
    /// to physical addresses.
    ///
    /// This function is unsafe because the caller must guarantee that the passed `phys_to_virt`
    /// closure is correct. Also, the passed `level_4_table` must point to the level 4 page table
    /// of a valid page table hierarchy. Otherwise this function might break memory safety, e.g.
    /// by writing to an illegal memory location.
    pub unsafe fn new(level_4_table: &'a mut PageTable, phys_to_virt: P) -> Self {
        Self {
            level_4_table,
            page_table_walker: PageTableWalker::new(phys_to_virt),
        }
    }

    /// Helper function for implementing Mapper. Safe to limit the scope of unsafe, see
    /// https://github.com/rust-lang/rfcs/pull/2585.
    fn map_to_1gib<A>(
        &mut self,
        page: Page<Size1GiB>,
        frame: PhysFrame<Size1GiB>,
        flags: PageTableFlags,
        allocator: &mut A,
    ) -> Result<MapperFlush<Size1GiB>, MapToError>
    where
        A: FrameAllocator<Size4KiB>,
    {
        let p4 = &mut self.level_4_table;
        let p3 = self
            .page_table_walker
            .create_next_table(&mut p4[page.p4_index()], allocator)?;

        if !p3[page.p3_index()].is_unused() {
            return Err(MapToError::PageAlreadyMapped);
        }
        p3[page.p3_index()].set_addr(frame.start_address(), flags | PageTableFlags::HUGE_PAGE);

        Ok(MapperFlush::new(page))
    }

    /// Helper function for implementing Mapper. Safe to limit the scope of unsafe, see
    /// https://github.com/rust-lang/rfcs/pull/2585.
    fn map_to_2mib<A>(
        &mut self,
        page: Page<Size2MiB>,
        frame: PhysFrame<Size2MiB>,
        flags: PageTableFlags,
        allocator: &mut A,
    ) -> Result<MapperFlush<Size2MiB>, MapToError>
    where
        A: FrameAllocator<Size4KiB>,
    {
        let p4 = &mut self.level_4_table;
        let p3 = self
            .page_table_walker
            .create_next_table(&mut p4[page.p4_index()], allocator)?;
        let p2 = self
            .page_table_walker
            .create_next_table(&mut p3[page.p3_index()], allocator)?;

        if !p2[page.p2_index()].is_unused() {
            return Err(MapToError::PageAlreadyMapped);
        }
        p2[page.p2_index()].set_addr(frame.start_address(), flags | PageTableFlags::HUGE_PAGE);

        Ok(MapperFlush::new(page))
    }

    /// Helper function for implementing Mapper. Safe to limit the scope of unsafe, see
    /// https://github.com/rust-lang/rfcs/pull/2585.
    fn map_to_4kib<A>(
        &mut self,
        page: Page<Size4KiB>,
        frame: PhysFrame<Size4KiB>,
        flags: PageTableFlags,
        allocator: &mut A,
    ) -> Result<MapperFlush<Size4KiB>, MapToError>
    where
        A: FrameAllocator<Size4KiB>,
    {
        let p4 = &mut self.level_4_table;
        let p3 = self
            .page_table_walker
            .create_next_table(&mut p4[page.p4_index()], allocator)?;
        let p2 = self
            .page_table_walker
            .create_next_table(&mut p3[page.p3_index()], allocator)?;
        let p1 = self
            .page_table_walker
            .create_next_table(&mut p2[page.p2_index()], allocator)?;

        if !p1[page.p1_index()].is_unused() {
            return Err(MapToError::PageAlreadyMapped);
        }
        p1[page.p1_index()].set_frame(frame, flags);

        Ok(MapperFlush::new(page))
    }
}

impl<'a, P: PhysToVirt> Mapper<Size1GiB> for MappedPageTable<'a, P> {
    unsafe fn map_to<A>(
        &mut self,
        page: Page<Size1GiB>,
        frame: PhysFrame<Size1GiB>,
        flags: PageTableFlags,
        allocator: &mut A,
    ) -> Result<MapperFlush<Size1GiB>, MapToError>
    where
        A: FrameAllocator<Size4KiB>,
    {
        self.map_to_1gib(page, frame, flags, allocator)
    }

    fn unmap(
        &mut self,
        page: Page<Size1GiB>,
    ) -> Result<(PhysFrame<Size1GiB>, MapperFlush<Size1GiB>), UnmapError> {
        let p4 = &mut self.level_4_table;
        let p3 = self
            .page_table_walker
            .next_table_mut(&mut p4[page.p4_index()])?;

        let p3_entry = &mut p3[page.p3_index()];
        let flags = p3_entry.flags();

        if !flags.contains(PageTableFlags::PRESENT) {
            return Err(UnmapError::PageNotMapped);
        }
        if !flags.contains(PageTableFlags::HUGE_PAGE) {
            return Err(UnmapError::ParentEntryHugePage);
        }

        let frame = PhysFrame::from_start_address(p3_entry.addr())
            .map_err(|()| UnmapError::InvalidFrameAddress(p3_entry.addr()))?;

        p3_entry.set_unused();
        Ok((frame, MapperFlush::new(page)))
    }

    fn update_flags(
        &mut self,
        page: Page<Size1GiB>,
        flags: PageTableFlags,
    ) -> Result<MapperFlush<Size1GiB>, FlagUpdateError> {
        let p4 = &mut self.level_4_table;
        let p3 = self
            .page_table_walker
            .next_table_mut(&mut p4[page.p4_index()])?;

        if p3[page.p3_index()].is_unused() {
            return Err(FlagUpdateError::PageNotMapped);
        }
        p3[page.p3_index()].set_flags(flags | PageTableFlags::HUGE_PAGE);

        Ok(MapperFlush::new(page))
    }

    fn translate_page(&self, page: Page<Size1GiB>) -> Result<PhysFrame<Size1GiB>, TranslateError> {
        let p4 = &self.level_4_table;
        let p3 = self.page_table_walker.next_table(&p4[page.p4_index()])?;

        let p3_entry = &p3[page.p3_index()];

        if p3_entry.is_unused() {
            return Err(TranslateError::PageNotMapped);
        }

        PhysFrame::from_start_address(p3_entry.addr())
            .map_err(|()| TranslateError::InvalidFrameAddress(p3_entry.addr()))
    }
}

impl<'a, P: PhysToVirt> Mapper<Size2MiB> for MappedPageTable<'a, P> {
    unsafe fn map_to<A>(
        &mut self,
        page: Page<Size2MiB>,
        frame: PhysFrame<Size2MiB>,
        flags: PageTableFlags,
        allocator: &mut A,
    ) -> Result<MapperFlush<Size2MiB>, MapToError>
    where
        A: FrameAllocator<Size4KiB>,
    {
        self.map_to_2mib(page, frame, flags, allocator)
    }

    fn unmap(
        &mut self,
        page: Page<Size2MiB>,
    ) -> Result<(PhysFrame<Size2MiB>, MapperFlush<Size2MiB>), UnmapError> {
        let p4 = &mut self.level_4_table;
        let p3 = self
            .page_table_walker
            .next_table_mut(&mut p4[page.p4_index()])?;
        let p2 = self
            .page_table_walker
            .next_table_mut(&mut p3[page.p3_index()])?;

        let p2_entry = &mut p2[page.p2_index()];
        let flags = p2_entry.flags();

        if !flags.contains(PageTableFlags::PRESENT) {
            return Err(UnmapError::PageNotMapped);
        }
        if !flags.contains(PageTableFlags::HUGE_PAGE) {
            return Err(UnmapError::ParentEntryHugePage);
        }

        let frame = PhysFrame::from_start_address(p2_entry.addr())
            .map_err(|()| UnmapError::InvalidFrameAddress(p2_entry.addr()))?;

        p2_entry.set_unused();
        Ok((frame, MapperFlush::new(page)))
    }

    fn update_flags(
        &mut self,
        page: Page<Size2MiB>,
        flags: PageTableFlags,
    ) -> Result<MapperFlush<Size2MiB>, FlagUpdateError> {
        let p4 = &mut self.level_4_table;
        let p3 = self
            .page_table_walker
            .next_table_mut(&mut p4[page.p4_index()])?;
        let p2 = self
            .page_table_walker
            .next_table_mut(&mut p3[page.p3_index()])?;

        if p2[page.p2_index()].is_unused() {
            return Err(FlagUpdateError::PageNotMapped);
        }

        p2[page.p2_index()].set_flags(flags | PageTableFlags::HUGE_PAGE);

        Ok(MapperFlush::new(page))
    }

    fn translate_page(&self, page: Page<Size2MiB>) -> Result<PhysFrame<Size2MiB>, TranslateError> {
        let p4 = &self.level_4_table;
        let p3 = self.page_table_walker.next_table(&p4[page.p4_index()])?;
        let p2 = self.page_table_walker.next_table(&p3[page.p3_index()])?;

        let p2_entry = &p2[page.p2_index()];

        if p2_entry.is_unused() {
            return Err(TranslateError::PageNotMapped);
        }

        PhysFrame::from_start_address(p2_entry.addr())
            .map_err(|()| TranslateError::InvalidFrameAddress(p2_entry.addr()))
    }
}

impl<'a, P: PhysToVirt> Mapper<Size4KiB> for MappedPageTable<'a, P> {
    unsafe fn map_to<A>(
        &mut self,
        page: Page<Size4KiB>,
        frame: PhysFrame<Size4KiB>,
        flags: PageTableFlags,
        allocator: &mut A,
    ) -> Result<MapperFlush<Size4KiB>, MapToError>
    where
        A: FrameAllocator<Size4KiB>,
    {
        self.map_to_4kib(page, frame, flags, allocator)
    }

    fn unmap(
        &mut self,
        page: Page<Size4KiB>,
    ) -> Result<(PhysFrame<Size4KiB>, MapperFlush<Size4KiB>), UnmapError> {
        let p4 = &mut self.level_4_table;
        let p3 = self
            .page_table_walker
            .next_table_mut(&mut p4[page.p4_index()])?;
        let p2 = self
            .page_table_walker
            .next_table_mut(&mut p3[page.p3_index()])?;
        let p1 = self
            .page_table_walker
            .next_table_mut(&mut p2[page.p2_index()])?;

        let p1_entry = &mut p1[page.p1_index()];

        let frame = p1_entry.frame().map_err(|err| match err {
            FrameError::FrameNotPresent => UnmapError::PageNotMapped,
            FrameError::HugeFrame => UnmapError::ParentEntryHugePage,
        })?;

        p1_entry.set_unused();
        Ok((frame, MapperFlush::new(page)))
    }

    fn update_flags(
        &mut self,
        page: Page<Size4KiB>,
        flags: PageTableFlags,
    ) -> Result<MapperFlush<Size4KiB>, FlagUpdateError> {
        let p4 = &mut self.level_4_table;
        let p3 = self
            .page_table_walker
            .next_table_mut(&mut p4[page.p4_index()])?;
        let p2 = self
            .page_table_walker
            .next_table_mut(&mut p3[page.p3_index()])?;
        let p1 = self
            .page_table_walker
            .next_table_mut(&mut p2[page.p2_index()])?;

        if p1[page.p1_index()].is_unused() {
            return Err(FlagUpdateError::PageNotMapped);
        }

        p1[page.p1_index()].set_flags(flags);

        Ok(MapperFlush::new(page))
    }

    fn translate_page(&self, page: Page<Size4KiB>) -> Result<PhysFrame<Size4KiB>, TranslateError> {
        let p4 = &self.level_4_table;
        let p3 = self.page_table_walker.next_table(&p4[page.p4_index()])?;
        let p2 = self.page_table_walker.next_table(&p3[page.p3_index()])?;
        let p1 = self.page_table_walker.next_table(&p2[page.p2_index()])?;

        let p1_entry = &p1[page.p1_index()];

        if p1_entry.is_unused() {
            return Err(TranslateError::PageNotMapped);
        }

        PhysFrame::from_start_address(p1_entry.addr())
            .map_err(|()| TranslateError::InvalidFrameAddress(p1_entry.addr()))
    }
}

impl<'a, P: PhysToVirt> MapperAllSizes for MappedPageTable<'a, P> {
    fn translate(&self, addr: VirtAddr) -> TranslateResult {
        let p4 = &self.level_4_table;
        let p3 = match self.page_table_walker.next_table(&p4[addr.p4_index()]) {
            Ok(page_table) => page_table,
            Err(PageTableWalkError::NotMapped) => return TranslateResult::PageNotMapped,
            Err(PageTableWalkError::MappedToHugePage) => {
                panic!("level 4 entry has huge page bit set")
            }
        };
        let p2 = match self.page_table_walker.next_table(&p3[addr.p3_index()]) {
            Ok(page_table) => page_table,
            Err(PageTableWalkError::NotMapped) => return TranslateResult::PageNotMapped,
            Err(PageTableWalkError::MappedToHugePage) => {
                let frame = PhysFrame::containing_address(p3[addr.p3_index()].addr());
                let offset = addr.as_u64() & 0o_777_777_7777;
                return TranslateResult::Frame1GiB { frame, offset };
            }
        };
        let p1 = match self.page_table_walker.next_table(&p2[addr.p2_index()]) {
            Ok(page_table) => page_table,
            Err(PageTableWalkError::NotMapped) => return TranslateResult::PageNotMapped,
            Err(PageTableWalkError::MappedToHugePage) => {
                let frame = PhysFrame::containing_address(p2[addr.p2_index()].addr());
                let offset = addr.as_u64() & 0o_777_7777;
                return TranslateResult::Frame2MiB { frame, offset };
            }
        };

        let p1_entry = &p1[addr.p1_index()];

        if p1_entry.is_unused() {
            return TranslateResult::PageNotMapped;
        }

        let frame = match PhysFrame::from_start_address(p1_entry.addr()) {
            Ok(frame) => frame,
            Err(()) => return TranslateResult::InvalidFrameAddress(p1_entry.addr()),
        };
        let offset = u64::from(addr.page_offset());
        TranslateResult::Frame4KiB { frame, offset }
    }
}

#[derive(Debug)]
struct PageTableWalker<P: PhysToVirt> {
    phys_to_virt: P,
}

impl<P: PhysToVirt> PageTableWalker<P> {
    pub unsafe fn new(phys_to_virt: P) -> Self {
        Self { phys_to_virt }
    }

    /// Internal helper function to get a reference to the page table of the next level.
    ///
    /// Returns `PageTableWalkError::NotMapped` if the entry is unused. Returns
    /// `PageTableWalkError::MappedToHugePage` if the `HUGE_PAGE` flag is set
    /// in the passed entry.
    fn next_table<'b>(
        &self,
        entry: &'b PageTableEntry,
    ) -> Result<&'b PageTable, PageTableWalkError> {
        let page_table_ptr = self.phys_to_virt.phys_to_virt(entry.frame()?);
        let page_table: &PageTable = unsafe { &*page_table_ptr };

        Ok(page_table)
    }

    /// Internal helper function to get a mutable reference to the page table of the next level.
    ///
    /// Returns `PageTableWalkError::NotMapped` if the entry is unused. Returns
    /// `PageTableWalkError::MappedToHugePage` if the `HUGE_PAGE` flag is set
    /// in the passed entry.
    fn next_table_mut<'b>(
        &self,
        entry: &'b mut PageTableEntry,
    ) -> Result<&'b mut PageTable, PageTableWalkError> {
        let page_table_ptr = self.phys_to_virt.phys_to_virt(entry.frame()?);
        let page_table: &mut PageTable = unsafe { &mut *page_table_ptr };

        Ok(page_table)
    }

    /// Internal helper function to create the page table of the next level if needed.
    ///
    /// If the passed entry is unused, a new frame is allocated from the given allocator, zeroed,
    /// and the entry is updated to that address. If the passed entry is already mapped, the next
    /// table is returned directly.
    ///
    /// Returns `MapToError::FrameAllocationFailed` if the entry is unused and the allocator
    /// returned `None`. Returns `MapToError::ParentEntryHugePage` if the `HUGE_PAGE` flag is set
    /// in the passed entry.
    fn create_next_table<'b, A>(
        &self,
        entry: &'b mut PageTableEntry,
        allocator: &mut A,
    ) -> Result<&'b mut PageTable, PageTableCreateError>
    where
        A: FrameAllocator<Size4KiB>,
    {
        let created;

        if entry.is_unused() {
            if let Some(frame) = allocator.allocate_frame() {
                entry.set_frame(frame, PageTableFlags::PRESENT | PageTableFlags::WRITABLE);
                created = true;
            } else {
                return Err(PageTableCreateError::FrameAllocationFailed);
            }
        } else {
            created = false;
        }

        let page_table = match self.next_table_mut(entry) {
            Err(PageTableWalkError::MappedToHugePage) => {
                Err(PageTableCreateError::MappedToHugePage)?
            }
            Err(PageTableWalkError::NotMapped) => panic!("entry should be mapped at this point"),
            Ok(page_table) => page_table,
        };

        if created {
            page_table.zero();
        }
        Ok(page_table)
    }
}

#[derive(Debug)]
enum PageTableWalkError {
    NotMapped,
    MappedToHugePage,
}

#[derive(Debug)]
enum PageTableCreateError {
    MappedToHugePage,
    FrameAllocationFailed,
}

impl From<PageTableCreateError> for MapToError {
    fn from(err: PageTableCreateError) -> Self {
        match err {
            PageTableCreateError::MappedToHugePage => MapToError::ParentEntryHugePage,
            PageTableCreateError::FrameAllocationFailed => MapToError::FrameAllocationFailed,
        }
    }
}

impl From<FrameError> for PageTableWalkError {
    fn from(err: FrameError) -> Self {
        match err {
            FrameError::HugeFrame => PageTableWalkError::MappedToHugePage,
            FrameError::FrameNotPresent => PageTableWalkError::NotMapped,
        }
    }
}

impl From<PageTableWalkError> for UnmapError {
    fn from(err: PageTableWalkError) -> Self {
        match err {
            PageTableWalkError::MappedToHugePage => UnmapError::ParentEntryHugePage,
            PageTableWalkError::NotMapped => UnmapError::PageNotMapped,
        }
    }
}

impl From<PageTableWalkError> for FlagUpdateError {
    fn from(err: PageTableWalkError) -> Self {
        match err {
            PageTableWalkError::MappedToHugePage => FlagUpdateError::ParentEntryHugePage,
            PageTableWalkError::NotMapped => FlagUpdateError::PageNotMapped,
        }
    }
}

impl From<PageTableWalkError> for TranslateError {
    fn from(err: PageTableWalkError) -> Self {
        match err {
            PageTableWalkError::MappedToHugePage => TranslateError::ParentEntryHugePage,
            PageTableWalkError::NotMapped => TranslateError::PageNotMapped,
        }
    }
}

/// Trait for converting a physical address to a virtual one.
///
/// This only works if the physical address space is somehow mapped to the virtual
/// address space, e.g. at an offset.
pub trait PhysToVirt {
    /// Translate the given physical frame to a virtual page table pointer.
    fn phys_to_virt(&self, phys_frame: PhysFrame) -> *mut PageTable;
}

impl<T> PhysToVirt for T
where
    T: Fn(PhysFrame) -> *mut PageTable,
{
    fn phys_to_virt(&self, phys_frame: PhysFrame) -> *mut PageTable {
        self(phys_frame)
    }
}