src/mm.c

#include "mm.h"

#include <stdatomic.h>
#include <stdint.h>

#include "alloc.h"
#include "dlog.h"

/* Keep macro alignment */
/* clang-format off */

#define MAP_FLAG_SYNC   0x01
#define MAP_FLAG_COMMIT 0x02

/* clang-format on */

/**
 * Calculates the size of the address space represented by a page table entry at
 * the given level.
 */
static inline size_t mm_entry_size(int level)
{
	return 1ull << (PAGE_BITS + level * PAGE_LEVEL_BITS);
}

/**
 * For a given virtual address, calculates the maximum (plus one) address that
 * can be represented by the same table at the given level.
 */
static inline vaddr_t mm_level_end(vaddr_t va, int level)
{
	size_t offset = PAGE_BITS + (level + 1) * PAGE_LEVEL_BITS;
	return ((va >> offset) + 1) << offset;
}

/**
 * For a given virtual address, calculates the index at which its entry is
 * stored in a table at the given level.
 */
static inline size_t mm_index(vaddr_t va, int level)
{
	vaddr_t v = va >> (PAGE_BITS + level * PAGE_LEVEL_BITS);
	return v & ((1ull << PAGE_LEVEL_BITS) - 1);
}

/**
 * Populates the provided page table entry with a reference to another table if
 * needed, that is, if it does not yet point to another table.
 *
 * Returns a pointer to the table the entry now points to.
 */
static pte_t *mm_populate_table_pte(pte_t *pte, int level, bool sync_alloc)
{
	pte_t *ntable;
	pte_t v = *pte;
	pte_t new_pte;
	size_t i;
	size_t inc;

	/* Just return pointer to table if it's already populated. */
	if (arch_mm_pte_is_table(v)) {
		return arch_mm_pte_to_table(v);
	}

	/* Allocate a new table. */
	ntable = (sync_alloc ? halloc_aligned : halloc_aligned_nosync)(
		PAGE_SIZE, PAGE_SIZE);
	if (!ntable) {
		dlog("Failed to allocate memory for page table\n");
		return NULL;
	}

	/* Determine template for new pte and its increment. */
	if (!arch_mm_pte_is_block(v)) {
		inc = 0;
		new_pte = arch_mm_absent_pte();
	} else {
		inc = mm_entry_size(level - 1);
		if (level == 1) {
			new_pte = arch_mm_block_to_page_pte(v);
		} else {
			new_pte = v;
		}
	}

	/* Initialise entries in the new table. */
	for (i = 0; i < PAGE_SIZE / sizeof(paddr_t); i++) {
		ntable[i] = new_pte;
		new_pte += inc;
	}

	/*
	 * Ensure initialisation is visible before updating the actual pte, then
	 * update it.
	 */
	atomic_thread_fence(memory_order_release);
	*pte = arch_mm_pa_to_table_pte((paddr_t)ntable);

	return ntable;
}

/**
 * Frees all page-table-related memory associated with the given pte at the
 * given level.
 */
static void mm_free_page_pte(pte_t pte, int level, bool sync)
{
	/* TODO: Implement.
	if (!arch_mm_pte_is_present(pte) || level < 1)
		return;
	*/
}

/**
 * Updates the page table at the given level to map the given virtual address
 * range to a physical range using the provided (architecture-specific)
 * attributes.
 *
 * This function calls itself recursively if it needs to update additional
 * levels, but the recursion is bound by the maximum number of levels in a page
 * table.
 */
static bool mm_map_level(vaddr_t va, vaddr_t va_end, paddr_t pa, uint64_t attrs,
			 pte_t *table, int level, int flags)
{
	size_t i = mm_index(va, level);
	vaddr_t va_level_end = mm_level_end(va, level);
	size_t entry_size = mm_entry_size(level);
	bool commit = flags & MAP_FLAG_COMMIT;
	bool sync = flags & MAP_FLAG_SYNC;

	/* Cap va_end so that we don't go over the current level max. */
	if (va_end > va_level_end) {
		va_end = va_level_end;
	}

	/* Fill each entry in the table. */
	while (va < va_end) {
		if (level == 0) {
			if (commit) {
				table[i] = arch_mm_pa_to_page_pte(pa, attrs);
			}
		} else if ((va_end - va) >= entry_size &&
			   arch_mm_is_block_allowed(level) &&
			   (va & (entry_size - 1)) == 0) {
			if (commit) {
				pte_t pte = table[i];
				table[i] = arch_mm_pa_to_block_pte(pa, attrs);
				/* TODO: Add barrier. How do we ensure this
				 * isn't in use by another CPU? Send IPI? */
				mm_free_page_pte(pte, level, sync);
			}
		} else {
			pte_t *nt =
				mm_populate_table_pte(table + i, level, sync);
			if (!nt) {
				return false;
			}

			if (!mm_map_level(va, va_end, pa, attrs, nt, level - 1,
					  flags)) {
				return false;
			}
		}

		va = (va + entry_size) & ~(entry_size - 1);
		pa = (pa + entry_size) & ~(entry_size - 1);
		i++;
	}

	return true;
}

/**
 * Invalidates the TLB for the given virtual address range.
 */
static void mm_invalidate_tlb(vaddr_t begin, vaddr_t end, bool stage1)
{
	if (stage1) {
		arch_mm_invalidate_stage1_range(begin, end);
	} else {
		arch_mm_invalidate_stage2_range(begin, end);
	}
}

/**
 * Updates the given table such that the given virtual address range is mapped
 * to the given physical address range in the architecture-agnostic mode
 * provided.
 */
bool mm_ptable_map(struct mm_ptable *t, vaddr_t begin, vaddr_t end,
		   paddr_t paddr, int mode)
{
	uint64_t attrs = arch_mm_mode_to_attrs(mode);
	int flags = (mode & MM_MODE_NOSYNC) ? 0 : MAP_FLAG_SYNC;
	int level = arch_mm_max_level(&t->arch);

	begin = arch_mm_clear_va(begin);
	end = arch_mm_clear_va(end + PAGE_SIZE - 1);
	paddr = arch_mm_clear_pa(paddr);

	/*
	 * Do it in two steps to prevent leaving the table in a halfway updated
	 * state. In such a two-step implementation, the table may be left with
	 * extra internal tables, but no different mapping on failure.
	 */
	if (!mm_map_level(begin, end, paddr, attrs, t->table, level, flags)) {
		return false;
	}

	mm_map_level(begin, end, paddr, attrs, t->table, level,
		     flags | MAP_FLAG_COMMIT);

	/* Invalidate the tlb. */
	mm_invalidate_tlb(begin, end, (mode & MM_MODE_STAGE1) != 0);

	return true;
}

/**
 * Updates the given table such that the given virtual address range is not
 * mapped to any physical address.
 */
bool mm_ptable_unmap(struct mm_ptable *t, vaddr_t begin, vaddr_t end, int mode)
{
	int flags = (mode & MM_MODE_NOSYNC) ? 0 : MAP_FLAG_SYNC;
	int level = arch_mm_max_level(&t->arch);

	begin = arch_mm_clear_va(begin);
	end = arch_mm_clear_va(end + PAGE_SIZE - 1);

	/* Also do updates in two steps, similarly to mm_ptable_map. */
	if (!mm_map_level(begin, end, begin, 0, t->table, level, flags)) {
		return false;
	}

	mm_map_level(begin, end, begin, 0, t->table, level,
		     flags | MAP_FLAG_COMMIT);

	/* Invalidate the tlb. */
	mm_invalidate_tlb(begin, end, (mode & MM_MODE_STAGE1) != 0);

	return true;
}

/**
 * Updates the given table such that a single virtual address page is mapped
 * to a single physical address page in the provided architecture-agnostic mode.
 */
bool mm_ptable_map_page(struct mm_ptable *t, vaddr_t va, paddr_t pa, int mode)
{
	size_t i;
	uint64_t attrs = arch_mm_mode_to_attrs(mode);
	pte_t *table = t->table;
	bool sync = !(mode & MM_MODE_NOSYNC);

	va = arch_mm_clear_va(va);
	pa = arch_mm_clear_pa(pa);

	for (i = arch_mm_max_level(&t->arch); i > 0; i--) {
		table = mm_populate_table_pte(table + mm_index(va, i), i, sync);
		if (!table) {
			return false;
		}
	}

	i = mm_index(va, 0);
	table[i] = arch_mm_pa_to_page_pte(pa, attrs);
	return true;
}

/**
 * Writes the given table to the debug log, calling itself recursively to
 * write sub-tables.
 */
static void mm_dump_table_recursive(pte_t *table, int level, int max_level)
{
	uint64_t i;
	for (i = 0; i < PAGE_SIZE / sizeof(pte_t); i++) {
		if (!arch_mm_pte_is_present(table[i])) {
			continue;
		}

		dlog("%*s%x: %x\n", 4 * (max_level - level), "", i, table[i]);
		if (!level) {
			continue;
		}

		if (arch_mm_pte_is_table(table[i])) {
			mm_dump_table_recursive(arch_mm_pte_to_table(table[i]),
						level - 1, max_level);
		}
	}
}

/**
 * Write the given table to the debug log.
 */
void mm_ptable_dump(struct mm_ptable *t)
{
	int max_level = arch_mm_max_level(&t->arch);
	mm_dump_table_recursive(t->table, max_level, max_level);
}

/**
 * Defragments the given page table by converting page table references to
 * blocks whenever possible.
 */
void mm_ptable_defrag(struct mm_ptable *t)
{
	/* TODO: Implement. */
}

/**
 * Initialises the given page table.
 */
bool mm_ptable_init(struct mm_ptable *t, int mode)
{
	size_t i;
	pte_t *table;

	if (mode & MM_MODE_NOSYNC) {
		table = halloc_aligned_nosync(PAGE_SIZE, PAGE_SIZE);
	} else {
		table = halloc_aligned(PAGE_SIZE, PAGE_SIZE);
	}

	if (!table) {
		return false;
	}

	for (i = 0; i < PAGE_SIZE / sizeof(pte_t); i++) {
		table[i] = arch_mm_absent_pte();
	}

	t->table = table;
	arch_mm_ptable_init(&t->arch);

	return true;
}