process: track ownership of pages in a more flexible way

src/kernel/process.c

@@ -58,6 +58,7 @@ void create_process(struct process *process_out) {
     process_out->p3_virtual_base[i] = 0;
     process_out->p2_virtual_bases[i] = 0;
     process_out->p1_virtual_bases[i] = 0;
+    process_out->owned_pages_bitmaps[i] = 0;
   }
 
   process_out->n_threads = 0;
@@ -67,7 +68,7 @@ void create_process(struct process *process_out) {
 
 void map_page_for_process(
   struct process *process, uint64_t physical_base,
-  void *virtual_base, int writable, int executable) {
+  void *virtual_base, int writable, int executable, int owned) {
 
   assert(physical_base % 4096 == 0)
 
@@ -87,9 +88,11 @@ void map_page_for_process(
     process->p3_virtual_base[p3i] = p2_pma | 0x7;
     process->p2_virtual_bases[p3i] = p2_vma;
     process->p1_virtual_bases[p3i] = heap_alloc(4096);
+    process->owned_pages_bitmaps[p3i] = heap_alloc(4096);
     for (int i = 0; i < 512; ++i) {
       p2_vma[i] = 0;
       process->p1_virtual_bases[p3i][i] = 0;
+      process->owned_pages_bitmaps[p3i][i] = 0;
     }
   }
 
@@ -99,8 +102,11 @@ void map_page_for_process(
     map_in_kernel_page_table(p1_pma, p1_vma, 1, 0);
     process->p2_virtual_bases[p3i][p2i] = p1_pma | 0x7;
     process->p1_virtual_bases[p3i][p2i] = p1_vma;
+    process->owned_pages_bitmaps[p3i][p2i] = heap_alloc(64);
     for (int i = 0; i < 512; ++i)
       p1_vma[i] = 0;
+    for (int i = 0; i < 64; ++i)
+      process->owned_pages_bitmaps[p3i][p2i][i] = 0;
   }
 
   assert(process->p1_virtual_bases[p3i][p2i][p1i] == 0)
@@ -109,6 +115,9 @@ void map_page_for_process(
     physical_base | 0x5 | (writable ? 0x2 : 0x0) |
     (executable ? 0 : 0x8000000000000000);
 
+  if (owned)
+    process->owned_pages_bitmaps[p3i][p2i][p1i / 8] |= 1 << (p1i % 8);
+
 }
 
 void unmap_page_for_process(
@@ -128,6 +137,12 @@ void unmap_page_for_process(
     process->p1_virtual_bases[p3i][p2i] &&
     process->p1_virtual_bases[p3i][p2i][p1i])
 
+  if (process->owned_pages_bitmaps[p3i][p2i][p1i / 8] & (1 << (p1i % 8))) {
+    process->owned_pages_bitmaps[p3i][p2i][p1i / 8] &= ~(1 << (p1i % 8));
+    uint64_t pma = process->p1_virtual_bases[p3i][p2i][p1i] & 0x7ffffffffffff000;
+    mark_physical_memory_free(pma, 4096);
+  }
+
   process->p1_virtual_bases[p3i][p2i][p1i] = 0;
 
 }
@@ -286,7 +301,7 @@ int load_elf(
 
       uint64_t pma = take_free_physical_page();
       map_page_for_process(
-        process, pma, virtual_start + i, writable, executable);
+        process, pma, virtual_start + i, writable, executable, 1);
 
       void *kvma = find_free_kernel_region(4096);
       map_in_kernel_page_table(pma, kvma, 1, 0);
@@ -377,15 +392,15 @@ void destroy_process(struct process *process) {
           for (int p1i = 0; p1i < 512; ++p1i) {
             uint64_t pma =
               process->p1_virtual_bases[p3i][p2i][p1i] & 0x7ffffffffffff000;
-            if (pma >= fb_physical_base &&
+            if (process->owned_pages_bitmaps[p3i][p2i][p1i / 8] & (1 << (p1i % 8)))
-                pma < fb_physical_base + fb_pitch * fb_height)
+              mark_physical_memory_free(pma, 4096);
-              continue;
-            mark_physical_memory_free(pma, 4096);
           }
           unmap_and_free_kernel_page(process->p1_virtual_bases[p3i][p2i]);
+          heap_dealloc(process->owned_pages_bitmaps[p3i][p2i], 64);
         }
       unmap_and_free_kernel_page(process->p2_virtual_bases[p3i]);
       heap_dealloc(process->p1_virtual_bases[p3i], 4096);
+      heap_dealloc(process->owned_pages_bitmaps[p3i], 4096);
     }
   unmap_and_free_kernel_page(process->p3_virtual_base);
   unmap_and_free_kernel_page(process->p4_virtual_base);
@@ -426,7 +441,7 @@ void create_thread(struct process *process, struct thread *thread_out) {
 
     uint64_t pma = take_free_physical_page();
     map_page_for_process(
-      process, pma, stack_bottom_vma + i * 4096, 1, 0);
+      process, pma, stack_bottom_vma + i * 4096, 1, 0, 1);
 
     void *kvma = find_free_kernel_region(4096);
     map_in_kernel_page_table(pma, kvma, 1, 0);
@@ -478,7 +493,7 @@ void syscall_map_framebuffer(struct framebuffer_info *info_out) {
     map_page_for_process(
       running_thread->process,
       fb_physical_base + i * 4096,
-      base + i * 4096, 1, 0);
+      base + i * 4096, 1, 0, 0);
 
   info_out->fb_base = base;
   info_out->fb_pitch = fb_pitch;
@@ -605,7 +620,7 @@ void *syscall_map_pages(uint64_t count) {
     map_page_for_process(
       running_thread->process,
       pma, vma + i * 4096,
-      1, 0);
+      1, 0, 1);
   }
 
   return vma;

src/kernel/process.h

@@ -46,6 +46,10 @@ struct process {
   uint64_t *p2_virtual_bases[512];
   uint64_t **p1_virtual_bases[512];
 
+  //also just bottom p3. bit set indicates we should free
+  //the physical page when we clean up this process.
+  uint8_t **owned_pages_bitmaps[512];
+
 };
 
 //returns 0 if that handle is not used.
@@ -71,7 +75,7 @@ void create_thread(struct process *process, struct thread *thread_out);
 //virtual base must be in bottom p3 and not zero.
 void map_page_for_process(
   struct process *process, uint64_t physical_base,
-  void *virtual_base, int writable, int executable);
+  void *virtual_base, int writable, int executable, int owned);
 
 //virtual base must be page-aligned, in bottom p3, and not zero.
 void unmap_page_for_process(