From 7984343abd6e3f7f2be45ac42de4e1eac1030330 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Sun, 5 May 2024 23:09:30 -0400
Subject: kernel: vm_fault: Refactor demand paging

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 sys/vm/vm_fault.c | 44 ++++++++++++++++++++++++++++----------------
 1 file changed, 28 insertions(+), 16 deletions(-)

diff --git a/sys/vm/vm_fault.c b/sys/vm/vm_fault.c
index ec733e8..d1a3e29 100644
--- a/sys/vm/vm_fault.c
+++ b/sys/vm/vm_fault.c
@@ -74,18 +74,36 @@ vm_find_mapping(vaddr_t addr)
     return NULL;
 }
 
+static int
+vm_demand_page(struct vm_mapping *mapping, vaddr_t va, vm_prot_t access_type)
+{
+    struct proc *td;
+    paddr_t pa_base;
+
+    int s;
+    size_t granule = vm_get_page_size();
+
+    /* Allocate physical memory if needed */
+    if (mapping->physmem_base == 0) {
+        pa_base = vm_alloc_pageframe(1);
+        mapping->physmem_base = pa_base;
+    } else {
+        pa_base = mapping->physmem_base;
+    }
+
+    td = this_td();
+    s = vm_map_create(td->addrsp, va, pa_base, access_type, granule);
+    return s;
+}
+
 int
 vm_fault(vaddr_t va, vm_prot_t access_type)
 {
-    struct proc *td = this_td();
     struct vm_mapping *mapping;
     struct vm_object *vmobj;
 
     size_t granule = vm_get_page_size();
-    vaddr_t va_base = va &= ~(granule - 1);
-
-    int s;
-    paddr_t pa_base;
+    vaddr_t va_base = va & ~(granule - 1);
 
     mapping = vm_find_mapping(va_base);
     if (mapping == NULL)
@@ -94,21 +112,15 @@ vm_fault(vaddr_t va, vm_prot_t access_type)
     if ((vmobj = mapping->vmobj) == NULL)
         /* Virtual memory object non-existent */
         return -1;
-    if (!vmobj->demand)
-        /* Demand paging not enabled for this object */
-        return -1;
     if ((access_type & ~mapping->prot) != 0)
         /* Invalid access type */
         return -1;
 
-    /* Allocate physical memory if needed */
-    if (mapping->physmem_base == 0) {
-        pa_base = vm_alloc_pageframe(1);
-        mapping->physmem_base = pa_base;
-    } else {
-        pa_base = mapping->physmem_base;
+    /* Can we perform demand paging? */
+    if (vmobj->demand) {
+        if (vm_demand_page(mapping, va_base, access_type) != 0)
+            return -1;
     }
 
-    s = vm_map_create(td->addrsp, va_base, pa_base, access_type, granule);
-    return s;
+    return 0;
 }
-- 
cgit v1.2.3