x86/page: add page flagging functions

arch/x86/mm/page.c

@@ -165,6 +165,50 @@ uintptr_t unmap_page(void *virt)
 	return phys;
 }
 
+enum pflags get_pflags(void *page)
+{
+	usize pd_index = ((uintptr_t)page >> PAGE_SHIFT) / 1024;
+	usize pt_index = ((uintptr_t)page >> PAGE_SHIFT) % 1024;
+
+	struct x86_page_directory_entry *pde = &X86_CURRENT_PD->entries[pd_index];
+	if (pde->huge) {
+		return *(unsigned long *)pde & ~PAGE_MASK;
+	} else if (pde->present) {
+		struct x86_page_table_entry *pte = &X86_CURRENT_PT(pd_index)->entries[pt_index];
+		return *(unsigned long *)pte & ~PAGE_MASK;
+	} else {
+		return 0;
+	}
+}
+
+int set_pflags(void *page, enum pflags pflags)
+{
+	usize pd_index = ((uintptr_t)page >> PAGE_SHIFT) / 1024;
+	usize pt_index = ((uintptr_t)page >> PAGE_SHIFT) % 1024;
+
+	struct x86_page_directory_entry *pde = &X86_CURRENT_PD->entries[pd_index];
+	if (pflags & P_HUGE) {
+		/* if the PDE referred to a Page Table, free it first */
+		if (pde->present && !pde->huge)
+			free_pages((void *)((uintptr_t)pde->shifted_address << PAGE_SHIFT));
+
+		unsigned long pde_raw = *(unsigned long *)pde;
+		pde_raw &= PAGE_MASK;
+		pde_raw |= (pflags & ~PAGE_MASK);
+		*(unsigned long *)pde = pde_raw;
+	} else if (pde->present) {
+		struct x86_page_table_entry *pte = X86_CURRENT_PTE(pd_index, pt_index);
+		unsigned long pte_raw = *(unsigned long *)pte;
+		pte_raw &= PAGE_MASK;
+		pte_raw |= (pflags & ~PAGE_MASK);
+		*(unsigned long *)pte = pte_raw;
+	} else {
+		return -EEXIST;
+	}
+
+	return 0;
+}
+
 void x86_isr_page_fault(trap_frame_t *frame, u32 error_code)
 {
 	void *address;

include/gay/mm.h

@@ -116,6 +116,32 @@ int map_page(uintptr_t phys, void *virt, enum pflags flags);
  */
 uintptr_t unmap_page(void *virt);
 
+/**
+ * @brief Get a page's flags in the page tables.
+ *
+ * @param page Page to get the flags of (if the page is in a hugepage area,
+ *	the flags for that hugepage will be returned with `P_HUGE = 1`)
+ * @return The flags, as currently stored in the page table structures
+ *	(but not necessarily applied if they have been modified and `vm_flush()`
+ *	has not been called yet!)
+ */
+enum pflags get_pflags(void *page);
+
+/**
+ * @brief Update a page's flags in the page tables.
+ * You should always use this in conjunction with `get_pflags()`, as in getting
+ * the flags first, then toggling the flags you need to, and then setting them
+ * in the tables again.  This is because this method will clear *any* previous
+ * flags.
+ *
+ * @param page Page to set flags for (if flags has `P_HUGE` set, must be
+ *	`HUGEPAGE_SIZE` aligned, otherwise `PAGE_SIZE` aligned)
+ * @param flags Flags to set
+ * @return 0 on success, or a negative value if either a page table allocation
+ *	failed or
+ */
+int set_pflags(void *page, enum pflags flags);
+
 /** @brief Flush the TLB. */
 void vm_flush(void);