kernel/vm: Consider cache overcommit status in copy_area and mprotect.

In copy_on_write_area, the copied cache should have the same overcommit
status as the original area, and in set_memory_protection, we shouldn't
change the committed size at all if the cache is overcommitting (otherwise,
we'd wind up shrinking cache's commit sizes below the actual number of
pages they contained in some cases.)

src/system/kernel/vm/vm.cpp

@@ -2733,7 +2733,8 @@ vm_copy_on_write_area(VMCache* lowerCache,
 	// deeper and we create a new cache inbetween.
 
 	// create an anonymous cache
-	status_t status = VMCacheFactory::CreateAnonymousCache(upperCache, false, 0,
+	status_t status = VMCacheFactory::CreateAnonymousCache(upperCache,
+		lowerCache->CanOvercommit(), 0,
 		lowerCache->GuardSize() / B_PAGE_SIZE,
 		dynamic_cast<VMAnonymousNoSwapCache*>(lowerCache) == NULL,
 		VM_PRIORITY_USER);
@@ -6317,7 +6318,7 @@ _user_set_memory_protection(void* _address, size_t size, uint32 protection)
 		cacheChainLocker.LockAllSourceCaches();
 
 		// Adjust the committed size, if necessary.
-		if (topCache->temporary) {
+		if (topCache->temporary && !topCache->CanOvercommit()) {
 			const bool becomesWritable = (protection & B_WRITE_AREA) != 0;
 			ssize_t commitmentChange = 0;
 			const off_t areaCacheBase = area->Base() - area->cache_offset;