vm: handle null vm_pages and empty zones in zone init

vm/zone.c

@@ -1,5 +1,6 @@
 #include <socks/locks.h>
 #include <socks/queue.h>
+#include <socks/memblock.h>
 #include <socks/types.h>
 #include <socks/vm.h>
 #include <socks/printk.h>
@@ -10,6 +11,9 @@ static vm_page_t *group_pages_into_block(vm_zone_t *z, phys_addr_t base, phys_ad
 	vm_page_t *first_page = NULL;
 	for (phys_addr_t i = base; i < limit; i += VM_PAGE_SIZE) {
 		vm_page_t *pg = vm_page_get(i);
+		if (!pg) {
+			continue;
+		}
 		/* p_flags is the only part of the page that has been
 		   initialised at this point. */
 
@@ -79,10 +83,6 @@ static void convert_region_to_blocks(vm_zone_t *zone,
 
 void vm_zone_init(vm_zone_t *z, const vm_zone_descriptor_t *zone_info)
 {
-	if (!vm_page_get(zone_info->zd_base)) {
-		return;
-	}
-	
 	memset(z, 0x0, sizeof *z);
 	memcpy(&z->z_info, zone_info, sizeof *zone_info);
 	z->z_lock = SPIN_LOCK_INIT;
@@ -93,13 +93,28 @@ void vm_zone_init(vm_zone_t *z, const vm_zone_descriptor_t *zone_info)
 	phys_addr_t block_start = zone_info->zd_base, block_end = zone_info->zd_limit;
 	int this_page_reserved = 0, last_page_reserved = -1;
 
-	for (uintptr_t i = zone_info->zd_base; i < zone_info->zd_limit; i += VM_PAGE_SIZE) {
+	phys_addr_t plimit = 0;
-		vm_page_t *pg = vm_page_get(i);
+	memblock_iter_t it;
-		if (!pg) {
+	for_each_mem_range (&it, 0x00, UINTPTR_MAX) {
-			break;
+		if (it.it_limit + 1 > plimit) {
+			plimit = it.it_limit + 1;
+		}
+	}
+
+	if (z->z_info.zd_limit > plimit) {
+		z->z_info.zd_limit = plimit;
+	}
+
+	size_t nr_pages_found = 0;
+	for (uintptr_t i = z->z_info.zd_base; i < z->z_info.zd_limit; i += VM_PAGE_SIZE) {
+		vm_page_t *pg = vm_page_get(i);
+
+		if (pg) {
+			nr_pages_found++;
+			this_page_reserved = (pg->p_flags & VM_PAGE_RESERVED) ? 1 : 0;
+		} else {
+			this_page_reserved = 1;
 		}
-		
-		this_page_reserved = (pg->p_flags & VM_PAGE_RESERVED) ? 1 : 0;
 
 		if (last_page_reserved == -1) {
 			last_page_reserved = this_page_reserved;
@@ -117,7 +132,11 @@ void vm_zone_init(vm_zone_t *z, const vm_zone_descriptor_t *zone_info)
 	}
 
 	if (block_start != block_end) {
-		convert_region_to_blocks(z, block_start, block_end + VM_PAGE_SIZE - 1, this_page_reserved);
+		/* either the entire zone is homogeneous (all free/all reserved) or the entire zone is empty. */
+		if (nr_pages_found > 0) {
+			/* the entire zone is homogeneous :) */
+			convert_region_to_blocks(z, block_start, block_end + VM_PAGE_SIZE - 1, this_page_reserved);
+		}
 	}
 
 	spin_unlock_irqrestore(&z->z_lock, flags);