From 399742cabf9484ce0e0308e588b382f001080798 Mon Sep 17 00:00:00 2001
From: Max Wash <mbswash@gmail.com>
Date: Sun, 15 Mar 2026 14:38:32 +0000
Subject: [PATCH] x86_64: pmap: implement pmap_remove

---
 arch/x86_64/pmap.c | 100 ++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 99 insertions(+), 1 deletion(-)

diff --git a/arch/x86_64/pmap.c b/arch/x86_64/pmap.c
index 13b9e14..b6bd2f5 100644
--- a/arch/x86_64/pmap.c
+++ b/arch/x86_64/pmap.c
@@ -241,6 +241,104 @@ static kern_status_t do_pmap_add(
 	return KERN_OK;
 }
 
+static kern_status_t do_pmap_remove(
+	pmap_t pmap,
+	virt_addr_t pv,
+	enum page_size size)
+{
+	unsigned int pml4t_index = BAD_INDEX, pdpt_index = BAD_INDEX,
+		     pd_index = BAD_INDEX, pt_index = BAD_INDEX;
+
+	switch (size) {
+	case PS_4K:
+		pml4t_index = (pv >> 39) & 0x1FF;
+		pdpt_index = (pv >> 30) & 0x1FF;
+		pd_index = (pv >> 21) & 0x1FF;
+		pt_index = (pv >> 12) & 0x1FF;
+		break;
+	case PS_2M:
+		pml4t_index = (pv >> 39) & 0x1FF;
+		pdpt_index = (pv >> 30) & 0x1FF;
+		pd_index = (pv >> 21) & 0x1FF;
+		break;
+	case PS_1G:
+		if (!can_use_gbpages) {
+			return KERN_UNSUPPORTED;
+		}
+		pml4t_index = (pv >> 39) & 0x1FF;
+		pdpt_index = (pv >> 30) & 0x1FF;
+		break;
+	default:
+		return KERN_INVALID_ARGUMENT;
+	}
+
+	/* 1. get PML4T (mandatory) */
+	struct pml4t *pml4t = vm_phys_to_virt(ENTRY_TO_PTR(pmap));
+	if (!pml4t) {
+		return KERN_OK;
+	}
+
+	/* 2. traverse PML4T, get PDPT (mandatory) */
+	struct pdpt *pdpt = NULL;
+	if (!pml4t->p_entries[pml4t_index]) {
+		return KERN_OK;
+	} else {
+		pdpt = vm_phys_to_virt(
+			ENTRY_TO_PTR(pml4t->p_entries[pml4t_index]));
+	}
+
+	/* if we're mapping a 1GiB page, we stop here */
+	if (size == PS_1G) {
+		if (pdpt->p_entries[pdpt_index] != 0) {
+			/* this slot points to a pdir, delete it.
+			   if this slot points to a hugepage, this does nothing
+			 */
+			delete_pdir(pdpt->p_entries[pdpt_index]);
+		}
+
+		pdpt->p_pages[pdpt_index] = 0;
+
+		return KERN_OK;
+	}
+
+	/* 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) {
+		/* entry is null, or points to a hugepage */
+		return KERN_OK;
+	} else {
+		pdir = vm_phys_to_virt(
+			ENTRY_TO_PTR(pdpt->p_entries[pdpt_index]));
+	}
+
+	/* if we're mapping a 2MiB page, we stop here */
+	if (size == PS_2M) {
+		if (pdir->p_entries[pd_index] != 0) {
+			/* this slot points to a ptab, delete it.
+			   if this slot points to a hugepage, this does nothing
+			 */
+			delete_ptab(pdir->p_entries[pd_index]);
+		}
+
+		pdir->p_pages[pd_index] = 0;
+		return KERN_OK;
+	}
+
+	/* 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_OK;
+	} else {
+		ptab = vm_phys_to_virt(ENTRY_TO_PTR(pdir->p_entries[pd_index]));
+	}
+
+	ptab->p_pages[pt_index] = 0;
+	return KERN_OK;
+}
+
 pmap_t get_kernel_pmap(void)
 {
 	return kernel_pmap;
@@ -404,7 +502,7 @@ kern_status_t pmap_add_block(
 
 kern_status_t pmap_remove(pmap_t pmap, virt_addr_t p)
 {
-	return KERN_OK;
+	return do_pmap_remove(pmap, p, PS_4K);
 }
 
 kern_status_t pmap_remove_range(pmap_t pmap, virt_addr_t p, size_t len)