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mm: properly implement page locking

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Matheus
2026-07-08 01:37:12 -03:00
parent af30088c0d
commit 1512b2f3c6
14 changed files with 123 additions and 45 deletions
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kernel-src/mm/mm.c
+36 -11
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@@ -161,7 +161,7 @@ int mm_full_page_in(mm_range_t *range, void *vaddr, page_t **resulting_page) {
return ENOMEM;
}
if (cacheable) {
if (cacheable && (range->mmuflags & ARCH_MMU_FLAGS_WRITE)) {
VOP_LOCK(range->vnode);
mm_cache_make_dirty(vn_page);
VOP_UNLOCK(range->vnode);
@@ -318,11 +318,20 @@ bool mm_handle_page_fault(void *addr, bool user, int actions) {
return status;
}
// TODO read-only permission checking for DMA
// space is expected to be locked on call.
static int lock_page(mm_space_t *space, void *vaddr) {
static int lock_page(mm_space_t *space, void *vaddr, int hint) {
// TODO: with a read hint, we could theoretically only partially page in.
mm_range_t *range = mm_get_range(space, vaddr);
if (!range)
if (!range ||
((hint & MM_GET_PHYSICAL_ADDRESS_FLAGS_LOCK_HINT_WRITE) && !(range->mmuflags & ARCH_MMU_FLAGS_WRITE)) ||
((hint & MM_GET_PHYSICAL_ADDRESS_FLAGS_LOCK_HINT_READ) && !(range->mmuflags & ARCH_MMU_FLAGS_READ)))
return EFAULT;
// since we cannot guarantee the mapping of a character device actually points to physical memory,
// we cannot reliably lock it. returning an error here also protects from trying to DMA into non-physical memory
// like the framebuffer.
// same thing applies to an abstract physical memory mapping.
if (((range->flags & MM_RANGE_FLAGS_FILE) && (range->vnode->type == V_TYPE_CHDEV)) || (range->flags & MM_RANGE_FLAGS_PHYSICAL))
return EFAULT;
// we need to make sure the address is fully paged in before locking, as it needs
@@ -350,7 +359,7 @@ void *mm_get_physical_address(void *addr, int flags) {
MUTEX_ACQUIRE(&space->lock);
void *physical;
if ((flags & MM_GET_PHYSICAL_ADDRESS_FLAGS_LOCK) && lock_page(space, aligned_addr)) {
if ((flags & MM_GET_PHYSICAL_ADDRESS_FLAGS_LOCK) && lock_page(space, aligned_addr, flags)) {
physical = NULL;
goto leave;
}
@@ -567,8 +576,6 @@ mm_context_t *mm_fork_context(mm_context_t *old_context) {
if (range->flags & MM_RANGE_FLAGS_FILE)
VOP_HOLD(range->vnode);
// copy any pages that are mapped
for (uintptr_t offset = 0; offset < new_range->size; offset += PAGE_SIZE) {
// XXX some types of mappings, like framebuffer shared mappings, will break if done this way
void *vaddr = (void *)((uintptr_t)new_range->start + offset);
@@ -576,12 +583,30 @@ mm_context_t *mm_fork_context(mm_context_t *old_context) {
if (phys == NULL)
continue;
if (arch_mmu_map(new_context->pagetable, phys, vaddr, new_range->mmuflags & ~ARCH_MMU_FLAGS_WRITE) == false)
goto error;
bool writeable = arch_mmu_iswritable(old_context->pagetable, vaddr);
bool private = !(range->flags & MM_RANGE_FLAGS_SHARED);
page_t *page = mm_get_page(phys);
if (mm_is_page_locked(page) && writeable && private) {
// the page is a private locked page, eagerly copy it to ensure fork/futex correctness
void *new_phys = mm_alloc_page(MEMORY_SECTION_DEFAULT);
if (new_phys == NULL)
goto error;
mm_hold_page(phys);
if (arch_mmu_map(new_context->pagetable, new_phys, vaddr, new_range->mmuflags) == false) {
mm_release_page(new_phys);
goto error;
}
arch_mmu_remap(old_context->pagetable, phys, vaddr, new_range->mmuflags & ~ARCH_MMU_FLAGS_WRITE);
memcpy(MAKE_HHDM(new_phys), MAKE_HHDM(phys), PAGE_SIZE);
} else {
// go through the normal CoW path
if (arch_mmu_map(new_context->pagetable, phys, vaddr, new_range->mmuflags & ~ARCH_MMU_FLAGS_WRITE) == false)
goto error;
mm_hold_page(phys);
arch_mmu_remap(old_context->pagetable, phys, vaddr, new_range->mmuflags & ~ARCH_MMU_FLAGS_WRITE);
}
}
rbtree = rbtree_successor(rbtree);