nova: fix memory leaks / invariant TSCs

- free up kernel memory of empty slabs (if already one empty slab is in
  place)
- free up more page table entries
- handle CPUs with invariant TSCs gracefully

  Genode/Nova running on CPUs without the invariant TSC feature may seem
  to 'hang'. The referenced commit of the nova branch fixes the issue
  for some older Intel CPUs.

Fixes #1615

repos/base-nova/ports/nova.hash

@@ -1 +1 @@
-2b256e6b852999be88a940c2dd211e40558213ed
+abcaff7f0e4a24e8a8fc7b8b023a82a544094767

repos/base-nova/ports/nova.port

@@ -4,7 +4,7 @@ DOWNLOADS := nova.git
 
 URL(nova) := https://github.com/alex-ab/NOVA.git
 # r9 branch
-REV(nova) := 27a42d2124a6631f58e7d925170b6b3bac36e2f8
+REV(nova) := e56cf80c88cac7d709dd2685e4966ddebb0feed5
 DIR(nova) := src/kernel/nova
 
 PATCHES   := $(wildcard $(REP_DIR)/patches/*.patch)

repos/base-nova/src/core/platform.cc

@@ -206,6 +206,14 @@ static void init_core_page_fault_handler()
 }
 
 
+static bool cpuid_invariant_tsc()
+{
+	unsigned long cpuid = 0x80000007, edx = 0;
+	asm volatile ("cpuid" : "+a" (cpuid), "=d" (edx) : : "ebx", "ecx");
+	return edx & 0x100;
+}
+
+
 /**************
  ** Platform **
  **************/
@@ -315,10 +323,14 @@ Platform::Platform() :
 	init_core_page_fault_handler();
 
 	if (verbose_boot_info) {
-		printf("Hypervisor %s VMX\n", hip->has_feature_vmx() ? "features" : "does not feature");
-		printf("Hypervisor %s SVM\n", hip->has_feature_svm() ? "features" : "does not feature");
+		if (hip->has_feature_vmx())
+			printf("Hypervisor features VMX\n");
+		if (hip->has_feature_svm())
+			printf("Hypervisor features SVM\n");
 		printf("Hypervisor reports %ux%u CPU%c - boot CPU is %lu\n",
 		       _cpus.width(), _cpus.height(), _cpus.total() > 1 ? 's' : ' ', boot_cpu());
+		if (!cpuid_invariant_tsc())
+			PWRN("CPU has no invariant TSC.");
 	}
 
 	/* initialize core allocators */