From d62920dcd07e947e9dc4228d10fa471bd6a6cb9c Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Tue, 16 Sep 2025 16:42:35 -0400
Subject: kern: vm: Implement lazy allocation for vm_map()

Introduce lazy allocation in the vm_map() function. When passing a zero
value to any of the base address fields of the map spec, allocate our
own memory.

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 src/sys/include/vm/map.h |  3 +++
 src/sys/vm/vm_map.c      | 17 +++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/src/sys/include/vm/map.h b/src/sys/include/vm/map.h
index 4e0f27e..69d7d73 100644
--- a/src/sys/include/vm/map.h
+++ b/src/sys/include/vm/map.h
@@ -44,6 +44,9 @@
  * @len: Length of mapping (4K aligned)
  * @prot: Memory protection flags (PROT_*)
  *
+ * XXX: If spec->va or spec->pa is a value of zero, an address
+ *      will be assigned and shared by both.
+ *
  * Returns zero on success, otherwise a less than zero value
  * on failure.
  */
diff --git a/src/sys/vm/vm_map.c b/src/sys/vm/vm_map.c
index 1b27a21..d8cb4b7 100644
--- a/src/sys/vm/vm_map.c
+++ b/src/sys/vm/vm_map.c
@@ -31,6 +31,7 @@
 #include <sys/param.h>
 #include <sys/errno.h>
 #include <sys/syslog.h>
+#include <vm/physseg.h>
 #include <vm/mmu.h>
 #include <vm/map.h>
 #include <vm/vm.h>
@@ -57,6 +58,22 @@ __vm_map(struct vm_vas *vas, struct mmu_map *spec, size_t len, int prot)
 
     /* Must be 4K aligned */
     len = ALIGN_UP(len, PSIZE);
+
+    /*
+     * If we encounter any address that is zero, we
+     * must assign our own.
+     */
+    if (spec->pa == 0 || spec->va == 0) {
+        spec->pa = vm_alloc_frame(len / PSIZE);
+        if (spec->va == 0)
+            spec->va = spec->pa;
+    }
+
+    if (spec->pa == 0) {
+        return -ENOMEM;
+    }
+
+    /* Must be on a 4K boundary */
     spec->va = ALIGN_DOWN(spec->va, PSIZE);
     spec->pa = ALIGN_DOWN(spec->pa, PSIZE);
 
-- 
cgit v1.2.3