pmap: add pmap_get to retrieve existing page table entries

arch/x86_64/pmap.c

@@ -136,6 +136,81 @@ static void delete_pdir(phys_addr_t pd)
 	kfree(pdir);
 }
 
+kern_status_t pmap_get(
+	pmap_t pmap,
+	virt_addr_t pv,
+	pfn_t *out_pfn,
+	vm_prot_t *out_prot)
+{
+	unsigned int pml4t_index = BAD_INDEX, pdpt_index = BAD_INDEX,
+		     pd_index = BAD_INDEX, pt_index = BAD_INDEX;
+
+	pml4t_index = (pv >> 39) & 0x1FF;
+	pdpt_index = (pv >> 30) & 0x1FF;
+	pd_index = (pv >> 21) & 0x1FF;
+	pt_index = (pv >> 12) & 0x1FF;
+
+	/* 1. get PML4T (mandatory) */
+	struct pml4t *pml4t = vm_phys_to_virt(ENTRY_TO_PTR(pmap));
+	if (!pml4t) {
+		return KERN_INVALID_ARGUMENT;
+	}
+
+	/* 2. traverse PML4T, get PDPT (mandatory) */
+	struct pdpt *pdpt = NULL;
+	if (!pml4t->p_entries[pml4t_index]) {
+		return KERN_NO_ENTRY;
+	} else {
+		pdpt = vm_phys_to_virt(
+			ENTRY_TO_PTR(pml4t->p_entries[pml4t_index]));
+	}
+
+	/* 3. traverse PDPT, get PDIR (optional, 4K and 2M only) */
+	struct pdir *pdir = NULL;
+	if (!pdpt->p_entries[pdpt_index]
+	    || pdpt->p_pages[pdpt_index] & PTE_PAGESIZE) {
+		return KERN_NO_ENTRY;
+	} else {
+		pdir = vm_phys_to_virt(
+			ENTRY_TO_PTR(pdpt->p_entries[pdpt_index]));
+	}
+
+	/* 4. traverse PDIR, get PTAB (optional, 4K only) */
+	struct ptab *ptab = NULL;
+	if (!pdir->p_entries[pd_index]
+	    || pdir->p_pages[pd_index] & PTE_PAGESIZE) {
+		/* entry is null, or points to a hugepage */
+		return KERN_NO_ENTRY;
+	} else {
+		ptab = vm_phys_to_virt(ENTRY_TO_PTR(pdir->p_entries[pd_index]));
+	}
+
+	uint64_t pte = ptab->p_pages[pt_index];
+	if (out_pfn) {
+		*out_pfn = PFN(pte);
+	}
+
+	if (out_prot) {
+		if (pte & PTE_PRESENT) {
+			*out_prot |= VM_PROT_USER;
+		}
+
+		if (pte & PTE_RW) {
+			*out_pfn |= (VM_PROT_READ | VM_PROT_WRITE);
+		}
+
+		if (pte & PTE_USR) {
+			*out_pfn |= VM_PROT_USER;
+		}
+
+		if (!(pte & PTE_NX)) {
+			*out_pfn |= VM_PROT_EXEC;
+		}
+	}
+
+	return KERN_OK;
+}
+
 static kern_status_t do_pmap_add(
 	pmap_t pmap,
 	virt_addr_t pv,