diff --git a/Makefile b/Makefile
index 0b866f65..9479c4d6 100644
--- a/Makefile
+++ b/Makefile
@@ -233,7 +233,7 @@ endif
 ifeq ($(HAVE_KVM), kvm)
 QEMU_PARAMS += -enable-kvm
 endif # HAVE_KVM
-QEMU_PARAMS += -m 8192
+QEMU_PARAMS += -m 128
 QEMU_PARAMS += -display none -vga none -vnc none
 QEMU_PARAMS += -serial stdio
 QEMU_PARAMS += -smp cpus=2
diff --git a/drivers/acpi/acpica/osl.c b/drivers/acpi/acpica/osl.c
index fac4be24..66a74e25 100644
--- a/drivers/acpi/acpica/osl.c
+++ b/drivers/acpi/acpica/osl.c
@@ -36,17 +36,35 @@
 
 #include "acpi.h"
 
+struct mapped_frame {
+    struct list_head list;
+    mfn_t mfn;
+    uint64_t refcount;
+};
+typedef struct mapped_frame mapped_frame_t;
+
+static list_head_t mapped_frames;
+
+static spinlock_t map_lock = SPINLOCK_INIT;
+
 /* General OS functions */
 
 ACPI_STATUS AcpiOsInitialize(void) {
     dprintk("ACPI OS Initialization:\n");
 
+    list_init(&mapped_frames);
     return AE_OK;
 }
 
 ACPI_STATUS AcpiOsTerminate(void) {
+    mapped_frame_t *frame;
+
     dprintk("ACPI OS Termination:\n");
 
+    list_for_each_entry (frame, &mapped_frames, list) {
+        list_unlink(&frame->list);
+        kfree(frame);
+    }
     return AE_OK;
 }
 
@@ -214,7 +232,7 @@ BOOLEAN AcpiOsReadable(void *Memory, ACPI_SIZE Length) {
     for (mfn_t mfn = virt_to_mfn(Memory); mfn <= virt_to_mfn((char *) Memory + Length);
          ++mfn) {
         success = false;
-        mem = mfn_to_virt_kern(mfn);
+        mem = mfn_to_virt_map(mfn);
         asm volatile("1: movq ( %[mem] ), %%rax; movq $1, %[success];"
                      "2:" ASM_EXTABLE(1b, 2b)
                      : [ success ] "=m"(success)
@@ -233,7 +251,7 @@ BOOLEAN AcpiOsWriteable(void *Memory, ACPI_SIZE Length) {
     for (mfn_t mfn = virt_to_mfn(Memory); mfn <= virt_to_mfn((char *) Memory + Length);
          ++mfn) {
         success = false;
-        mem = mfn_to_virt_kern(mfn);
+        mem = mfn_to_virt_map(mfn);
         asm volatile("1: orq $0, ( %[mem] ); movq $1, %[success];"
                      "2:" ASM_EXTABLE(1b, 2b)
                      : [ success ] "=m"(success), [ mem ] "=r"(mem)
@@ -246,20 +264,52 @@ BOOLEAN AcpiOsWriteable(void *Memory, ACPI_SIZE Length) {
     return success;
 }
 
+static inline mapped_frame_t *find_mapped_frame(mfn_t mfn) {
+    mapped_frame_t *frame;
+
+    list_for_each_entry (frame, &mapped_frames, list) {
+        if (frame->mfn == mfn)
+            return frame;
+    }
+
+    return NULL;
+}
+
+static inline void new_mapped_frame(mfn_t mfn) {
+    mapped_frame_t *frame = kzalloc(sizeof(*frame));
+    frame->mfn = mfn;
+    frame->refcount = 1;
+    list_add(&frame->list, &mapped_frames);
+}
+
 void *AcpiOsMapMemory(ACPI_PHYSICAL_ADDRESS PhysicalAddress, ACPI_SIZE Length) {
     unsigned offset = PhysicalAddress & ~PAGE_MASK;
     unsigned num_pages = ((offset + Length) / PAGE_SIZE) + 1;
     mfn_t mfn = paddr_to_mfn(PhysicalAddress);
     void *va = NULL;
 
+    spin_lock(&map_lock);
     for (unsigned i = 0; i < num_pages; i++, mfn++) {
-        void *_va = kmap_4k(mfn, L1_PROT);
-        if (!_va)
-            return NULL;
+        mapped_frame_t *frame = find_mapped_frame(mfn);
+        void *_va;
+
+        if (!frame) {
+            _va = mmap_4k(mfn, L1_PROT);
+            if (!_va) {
+                spin_unlock(&map_lock);
+                return NULL;
+            }
+            new_mapped_frame(mfn);
+        }
+        else {
+            frame->refcount++;
+            _va = mfn_to_virt_map(mfn);
+        }
 
         if (!va)
             va = _ptr(_ul(_va) + offset);
     }
+    spin_unlock(&map_lock);
 
     return va;
 }
@@ -269,8 +319,19 @@ void AcpiOsUnmapMemory(void *LogicalAddress, ACPI_SIZE Length) {
     unsigned num_pages = ((offset + Length) / PAGE_SIZE) + 1;
     mfn_t mfn = virt_to_mfn(LogicalAddress);
 
-    for (unsigned i = 0; i < num_pages; i++, mfn++)
-        vunmap(mfn_to_virt_kern(mfn), PAGE_ORDER_4K);
+    spin_lock(&map_lock);
+    for (unsigned i = 0; i < num_pages; i++, mfn++) {
+        mapped_frame_t *frame = find_mapped_frame(mfn);
+        BUG_ON(!frame || frame->refcount == 0);
+
+        if (--frame->refcount > 0)
+            continue;
+
+        vunmap(mfn_to_virt_map(mfn), PAGE_ORDER_4K);
+        list_unlink(&frame->list);
+        kfree(frame);
+    }
+    spin_unlock(&map_lock);
 }
 
 /* Task management functions */