Patchwork [V14,09/17] xen: Introduce the Xen mapcache

login
register
mail settings
Submitter Anthony PERARD
Date April 20, 2011, 4:41 p.m.
Message ID <1303317726-31855-10-git-send-email-anthony.perard@citrix.com>
Download mbox | patch
Permalink /patch/92247/
State New
Headers show

Comments

Anthony PERARD - April 20, 2011, 4:41 p.m.
From: Jun Nakajima <jun.nakajima@intel.com>

On IA32 host or IA32 PAE host, at present, generally, we can't create
an HVM guest with more than 2G memory, because generally it's almost
impossible for Qemu to find a large enough and consecutive virtual
address space to map an HVM guest's whole physical address space.
The attached patch fixes this issue using dynamic mapping based on
little blocks of memory.

Each call to qemu_get_ram_ptr makes a call to qemu_map_cache with the
lock option, so mapcache will not unmap these ram_ptr.

Blocks that do not belong to the RAM, but usually to a device ROM or to
a framebuffer, are handled in a separate function. So the whole RAMBlock
can be map.

Signed-off-by: Jun Nakajima <jun.nakajima@intel.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
---
 Makefile.target     |    3 +
 configure           |    3 +
 exec.c              |   48 +++++++-
 hw/xen.h            |   13 ++
 hw/xen_common.h     |    9 ++
 trace-events        |   10 ++
 xen-all.c           |   66 ++++++++++
 xen-mapcache-stub.c |   44 +++++++
 xen-mapcache.c      |  349 +++++++++++++++++++++++++++++++++++++++++++++++++++
 xen-mapcache.h      |   37 ++++++
 xen-stub.c          |    4 +
 11 files changed, 582 insertions(+), 4 deletions(-)
 create mode 100644 xen-mapcache-stub.c
 create mode 100644 xen-mapcache.c
 create mode 100644 xen-mapcache.h

Patch

diff --git a/Makefile.target b/Makefile.target
index 6b2a41c..c964c0d 100644
--- a/Makefile.target
+++ b/Makefile.target
@@ -214,8 +214,11 @@  else
   CONFIG_NO_XEN = y
 endif
 # xen support
+CONFIG_NO_XEN_MAPCACHE = $(if $(subst n,,$(CONFIG_XEN_MAPCACHE)),n,y)
 obj-i386-$(CONFIG_XEN) += xen-all.o
 obj-$(CONFIG_NO_XEN) += xen-stub.o
+obj-i386-$(CONFIG_XEN_MAPCACHE) += xen-mapcache.o
+obj-$(CONFIG_NO_XEN_MAPCACHE) += xen-mapcache-stub.o
 
 # Inter-VM PCI shared memory
 CONFIG_IVSHMEM =
diff --git a/configure b/configure
index 98b79e2..340a810 100755
--- a/configure
+++ b/configure
@@ -3283,6 +3283,9 @@  case "$target_arch2" in
   i386|x86_64)
     if test "$xen" = "yes" -a "$target_softmmu" = "yes" ; then
       echo "CONFIG_XEN=y" >> $config_target_mak
+      if test "$cpu" = "i386" -o "$cpu" = "x86_64"; then
+          echo "CONFIG_XEN_MAPCACHE=y" >> $config_target_mak
+      fi
     fi
 esac
 case "$target_arch2" in
diff --git a/exec.c b/exec.c
index b1ee52a..3f895eb 100644
--- a/exec.c
+++ b/exec.c
@@ -32,6 +32,7 @@ 
 #include "hw/qdev.h"
 #include "osdep.h"
 #include "kvm.h"
+#include "hw/xen.h"
 #include "qemu-timer.h"
 #if defined(CONFIG_USER_ONLY)
 #include <qemu.h>
@@ -51,6 +52,8 @@ 
 #include <libutil.h>
 #endif
 #endif
+#else /* !CONFIG_USER_ONLY */
+#include "xen-mapcache.h"
 #endif
 
 //#define DEBUG_TB_INVALIDATE
@@ -2872,6 +2875,7 @@  ram_addr_t qemu_ram_alloc_from_ptr(DeviceState *dev, const char *name,
         }
     }
 
+    new_block->offset = find_ram_offset(size);
     if (host) {
         new_block->host = host;
         new_block->flags |= RAM_PREALLOC_MASK;
@@ -2894,13 +2898,15 @@  ram_addr_t qemu_ram_alloc_from_ptr(DeviceState *dev, const char *name,
                                    PROT_EXEC|PROT_READ|PROT_WRITE,
                                    MAP_SHARED | MAP_ANONYMOUS, -1, 0);
 #else
-            new_block->host = qemu_vmalloc(size);
+            if (xen_mapcache_enabled()) {
+                xen_ram_alloc(new_block->offset, size);
+            } else {
+                new_block->host = qemu_vmalloc(size);
+            }
 #endif
             qemu_madvise(new_block->host, size, QEMU_MADV_MERGEABLE);
         }
     }
-
-    new_block->offset = find_ram_offset(size);
     new_block->length = size;
 
     QLIST_INSERT_HEAD(&ram_list.blocks, new_block, next);
@@ -2945,7 +2951,11 @@  void qemu_ram_free(ram_addr_t addr)
 #if defined(TARGET_S390X) && defined(CONFIG_KVM)
                 munmap(block->host, block->length);
 #else
-                qemu_vfree(block->host);
+                if (xen_mapcache_enabled()) {
+                    qemu_invalidate_entry(block->host);
+                } else {
+                    qemu_vfree(block->host);
+                }
 #endif
             }
             qemu_free(block);
@@ -3034,6 +3044,16 @@  void *qemu_get_ram_ptr(ram_addr_t addr)
                 QLIST_REMOVE(block, next);
                 QLIST_INSERT_HEAD(&ram_list.blocks, block, next);
             }
+            if (xen_mapcache_enabled()) {
+                /* We need to check if the requested address is in the RAM
+                 * because we don't want to map the entire memory in QEMU.
+                 */
+                if (block->offset == 0) {
+                    return qemu_map_cache(addr, 0, 1);
+                } else if (block->host == NULL) {
+                    block->host = xen_map_block(block->offset, block->length);
+                }
+            }
             return block->host + (addr - block->offset);
         }
     }
@@ -3053,6 +3073,16 @@  void *qemu_safe_ram_ptr(ram_addr_t addr)
 
     QLIST_FOREACH(block, &ram_list.blocks, next) {
         if (addr - block->offset < block->length) {
+            if (xen_mapcache_enabled()) {
+                /* We need to check if the requested address is in the RAM
+                 * because we don't want to map the entire memory in QEMU.
+                 */
+                if (block->offset == 0) {
+                    return qemu_map_cache(addr, 0, 1);
+                } else if (block->host == NULL) {
+                    block->host = xen_map_block(block->offset, block->length);
+                }
+            }
             return block->host + (addr - block->offset);
         }
     }
@@ -3069,11 +3099,21 @@  int qemu_ram_addr_from_host(void *ptr, ram_addr_t *ram_addr)
     uint8_t *host = ptr;
 
     QLIST_FOREACH(block, &ram_list.blocks, next) {
+        /* This case append when the block is not mapped. */
+        if (block->host == NULL) {
+            continue;
+        }
         if (host - block->host < block->length) {
             *ram_addr = block->offset + (host - block->host);
             return 0;
         }
     }
+
+    if (xen_mapcache_enabled()) {
+        *ram_addr = qemu_ram_addr_from_mapcache(ptr);
+        return 0;
+    }
+
     return -1;
 }
 
diff --git a/hw/xen.h b/hw/xen.h
index 9f00c0b..6245b38 100644
--- a/hw/xen.h
+++ b/hw/xen.h
@@ -31,6 +31,15 @@  static inline int xen_enabled(void)
 #endif
 }
 
+static inline int xen_mapcache_enabled(void)
+{
+#ifdef CONFIG_XEN_MAPCACHE
+    return xen_enabled();
+#else
+    return 0;
+#endif
+}
+
 int xen_pci_slot_get_pirq(PCIDevice *pci_dev, int irq_num);
 void xen_piix3_set_irq(void *opaque, int irq_num, int level);
 void xen_piix_pci_write_config_client(uint32_t address, uint32_t val, int len);
@@ -41,6 +50,10 @@  int xen_init(void);
 int xen_hvm_init(void);
 void xen_vcpu_init(void);
 
+#if defined(NEED_CPU_H) && !defined(CONFIG_USER_ONLY)
+void xen_ram_alloc(ram_addr_t ram_addr, ram_addr_t size);
+#endif
+
 #if defined(CONFIG_XEN) && CONFIG_XEN_CTRL_INTERFACE_VERSION < 400
 #  define HVM_MAX_VCPUS 32
 #endif
diff --git a/hw/xen_common.h b/hw/xen_common.h
index 47b8afe..dd3e896 100644
--- a/hw/xen_common.h
+++ b/hw/xen_common.h
@@ -63,6 +63,15 @@  static inline int xc_fd(int xen_xc)
 }
 
 
+static inline int xc_domain_populate_physmap_exact
+    (XenXC xc_handle, uint32_t domid, unsigned long nr_extents,
+     unsigned int extent_order, unsigned int mem_flags, xen_pfn_t *extent_start)
+{
+    return xc_domain_memory_populate_physmap
+        (xc_handle, domid, nr_extents, extent_order, mem_flags, extent_start);
+}
+
+
 /* Xen 4.1 */
 #else
 
diff --git a/trace-events b/trace-events
index 703b745..27e5134 100644
--- a/trace-events
+++ b/trace-events
@@ -360,3 +360,13 @@  disable milkymist_uart_pulse_irq_tx(void) "Pulse IRQ TX"
 # hw/milkymist-vgafb.c
 disable milkymist_vgafb_memory_read(uint32_t addr, uint32_t value) "addr %08x value %08x"
 disable milkymist_vgafb_memory_write(uint32_t addr, uint32_t value) "addr %08x value %08x"
+
+# xen-all.c
+disable xen_ram_alloc(unsigned long ram_addr, unsigned long size) "requested: %#lx, size %#lx"
+
+# xen-mapcache.c
+disable qemu_map_cache(uint64_t phys_addr) "want %#"PRIx64""
+disable qemu_remap_bucket(uint64_t index) "index %#"PRIx64""
+disable qemu_map_cache_return(void* ptr) "%p"
+disable xen_map_block(uint64_t phys_addr, uint64_t size) "%#"PRIx64", size %#"PRIx64""
+disable xen_unmap_block(void* addr, unsigned long size) "%p, size %#lx"
diff --git a/xen-all.c b/xen-all.c
index bb809ef..cb01ab9 100644
--- a/xen-all.c
+++ b/xen-all.c
@@ -10,6 +10,9 @@ 
 #include "hw/xen_common.h"
 #include "hw/xen_backend.h"
 
+#include "xen-mapcache.h"
+#include "trace.h"
+
 /* Xen specific function for piix pci */
 
 int xen_pci_slot_get_pirq(PCIDevice *pci_dev, int irq_num)
@@ -52,6 +55,65 @@  qemu_irq *xen_interrupt_controller_init(void)
     return qemu_allocate_irqs(xen_set_irq, NULL, 16);
 }
 
+/* Memory Ops */
+
+static void xen_ram_init(ram_addr_t ram_size)
+{
+    RAMBlock *new_block;
+    ram_addr_t below_4g_mem_size, above_4g_mem_size = 0;
+
+    new_block = qemu_mallocz(sizeof (*new_block));
+    pstrcpy(new_block->idstr, sizeof (new_block->idstr), "xen.ram");
+    new_block->host = NULL;
+    new_block->offset = 0;
+    new_block->length = ram_size;
+
+    QLIST_INSERT_HEAD(&ram_list.blocks, new_block, next);
+
+    ram_list.phys_dirty = qemu_realloc(ram_list.phys_dirty,
+                                       new_block->length >> TARGET_PAGE_BITS);
+    memset(ram_list.phys_dirty + (new_block->offset >> TARGET_PAGE_BITS),
+           0xff, new_block->length >> TARGET_PAGE_BITS);
+
+    if (ram_size >= 0xe0000000 ) {
+        above_4g_mem_size = ram_size - 0xe0000000;
+        below_4g_mem_size = 0xe0000000;
+    } else {
+        below_4g_mem_size = ram_size;
+    }
+
+    cpu_register_physical_memory(0, below_4g_mem_size, new_block->offset);
+#if TARGET_PHYS_ADDR_BITS > 32
+    if (above_4g_mem_size > 0) {
+        cpu_register_physical_memory(0x100000000ULL, above_4g_mem_size,
+                                     new_block->offset + below_4g_mem_size);
+    }
+#endif
+}
+
+void xen_ram_alloc(ram_addr_t ram_addr, ram_addr_t size)
+{
+    unsigned long nr_pfn;
+    xen_pfn_t *pfn_list;
+    int i;
+
+    trace_xen_ram_alloc(ram_addr, size);
+
+    nr_pfn = size >> TARGET_PAGE_BITS;
+    pfn_list = qemu_malloc(sizeof (*pfn_list) * nr_pfn);
+
+    for (i = 0; i < nr_pfn; i++) {
+        pfn_list[i] = (ram_addr >> TARGET_PAGE_BITS) + i;
+    }
+
+    if (xc_domain_populate_physmap_exact(xen_xc, xen_domid, nr_pfn, 0, 0, pfn_list)) {
+        hw_error("xen: failed to populate ram at %lx", ram_addr);
+    }
+
+    qemu_free(pfn_list);
+}
+
+
 /* VCPU Operations, MMIO, IO ring ... */
 
 static void xen_reset_vcpu(void *opaque)
@@ -86,5 +148,9 @@  int xen_init(void)
 
 int xen_hvm_init(void)
 {
+    /* Init RAM management */
+    qemu_map_cache_init();
+    xen_ram_init(ram_size);
+
     return 0;
 }
diff --git a/xen-mapcache-stub.c b/xen-mapcache-stub.c
new file mode 100644
index 0000000..7c14b3d
--- /dev/null
+++ b/xen-mapcache-stub.c
@@ -0,0 +1,44 @@ 
+/*
+ * Copyright (C) 2011       Citrix Ltd.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#include "config.h"
+
+#include "exec-all.h"
+#include "qemu-common.h"
+#include "cpu-common.h"
+#include "xen-mapcache.h"
+
+void qemu_map_cache_init(void)
+{
+}
+
+uint8_t *qemu_map_cache(target_phys_addr_t phys_addr, target_phys_addr_t size, uint8_t lock)
+{
+    return qemu_get_ram_ptr(phys_addr);
+}
+
+void qemu_map_cache_unlock(void *buffer)
+{
+}
+
+ram_addr_t qemu_ram_addr_from_mapcache(void *ptr)
+{
+    return -1;
+}
+
+void qemu_invalidate_map_cache(void)
+{
+}
+
+void qemu_invalidate_entry(uint8_t *buffer)
+{
+}
+uint8_t *xen_map_block(target_phys_addr_t phys_addr, target_phys_addr_t size)
+{
+    return NULL;
+}
diff --git a/xen-mapcache.c b/xen-mapcache.c
new file mode 100644
index 0000000..a539358
--- /dev/null
+++ b/xen-mapcache.c
@@ -0,0 +1,349 @@ 
+/*
+ * Copyright (C) 2011       Citrix Ltd.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#include "config.h"
+
+#include <sys/resource.h>
+
+#include "hw/xen_backend.h"
+#include "blockdev.h"
+
+#include <xen/hvm/params.h>
+#include <sys/mman.h>
+
+#include "xen-mapcache.h"
+#include "trace.h"
+
+
+//#define MAPCACHE_DEBUG
+
+#ifdef MAPCACHE_DEBUG
+#  define DPRINTF(fmt, ...) do { \
+    fprintf(stderr, "xen_mapcache: " fmt, ## __VA_ARGS__); \
+} while (0)
+#else
+#  define DPRINTF(fmt, ...) do { } while (0)
+#endif
+
+#if defined(__i386__)
+#  define MCACHE_BUCKET_SHIFT 16
+#elif defined(__x86_64__)
+#  define MCACHE_BUCKET_SHIFT 20
+#endif
+#define MCACHE_BUCKET_SIZE (1UL << MCACHE_BUCKET_SHIFT)
+
+#define BITS_PER_LONG (sizeof(long) * 8)
+#define BITS_TO_LONGS(bits) (((bits) + BITS_PER_LONG - 1) / BITS_PER_LONG)
+#define DECLARE_BITMAP(name, bits) unsigned long name[BITS_TO_LONGS(bits)]
+
+typedef struct MapCacheEntry {
+    target_phys_addr_t paddr_index;
+    uint8_t *vaddr_base;
+    DECLARE_BITMAP(valid_mapping, MCACHE_BUCKET_SIZE >> XC_PAGE_SHIFT);
+    uint8_t lock;
+    struct MapCacheEntry *next;
+} MapCacheEntry;
+
+typedef struct MapCacheRev {
+    uint8_t *vaddr_req;
+    target_phys_addr_t paddr_index;
+    QTAILQ_ENTRY(MapCacheRev) next;
+} MapCacheRev;
+
+typedef struct MapCache {
+    MapCacheEntry *entry;
+    unsigned long nr_buckets;
+    QTAILQ_HEAD(map_cache_head, MapCacheRev) locked_entries;
+
+    /* For most cases (>99.9%), the page address is the same. */
+    target_phys_addr_t last_address_index;
+    uint8_t *last_address_vaddr;
+    unsigned long max_mcache_size;
+    unsigned int mcache_bucket_shift;
+} MapCache;
+
+static MapCache *mapcache;
+
+static inline int test_bit(unsigned int bit, const unsigned long *map)
+{
+    return !!((map)[(bit) / BITS_PER_LONG] & (1UL << ((bit) % BITS_PER_LONG)));
+}
+
+void qemu_map_cache_init(void)
+{
+    unsigned long size;
+    struct rlimit rlimit_as;
+
+    mapcache = qemu_mallocz(sizeof (MapCache));
+
+    QTAILQ_INIT(&mapcache->locked_entries);
+    mapcache->last_address_index = -1;
+
+    getrlimit(RLIMIT_AS, &rlimit_as);
+    rlimit_as.rlim_cur = rlimit_as.rlim_max;
+    setrlimit(RLIMIT_AS, &rlimit_as);
+    mapcache->max_mcache_size = rlimit_as.rlim_max;
+
+    mapcache->nr_buckets =
+        (((mapcache->max_mcache_size >> XC_PAGE_SHIFT) +
+          (1UL << (MCACHE_BUCKET_SHIFT - XC_PAGE_SHIFT)) - 1) >>
+         (MCACHE_BUCKET_SHIFT - XC_PAGE_SHIFT));
+
+    size = mapcache->nr_buckets * sizeof (MapCacheEntry);
+    size = (size + XC_PAGE_SIZE - 1) & ~(XC_PAGE_SIZE - 1);
+    DPRINTF("qemu_map_cache_init, nr_buckets = %lx size %lu\n", mapcache->nr_buckets, size);
+    mapcache->entry = qemu_mallocz(size);
+}
+
+static void qemu_remap_bucket(MapCacheEntry *entry,
+                              target_phys_addr_t size,
+                              target_phys_addr_t address_index)
+{
+    uint8_t *vaddr_base;
+    xen_pfn_t *pfns;
+    int *err;
+    unsigned int i, j;
+    target_phys_addr_t nb_pfn = size >> XC_PAGE_SHIFT;
+
+    trace_qemu_remap_bucket(address_index);
+
+    pfns = qemu_mallocz(nb_pfn * sizeof (xen_pfn_t));
+    err = qemu_mallocz(nb_pfn * sizeof (int));
+
+    if (entry->vaddr_base != NULL) {
+        if (munmap(entry->vaddr_base, size) != 0) {
+            perror("unmap fails");
+            exit(-1);
+        }
+    }
+
+    for (i = 0; i < nb_pfn; i++) {
+        pfns[i] = (address_index << (MCACHE_BUCKET_SHIFT-XC_PAGE_SHIFT)) + i;
+    }
+
+    vaddr_base = xc_map_foreign_bulk(xen_xc, xen_domid, PROT_READ|PROT_WRITE,
+                                     pfns, err, nb_pfn);
+    if (vaddr_base == NULL) {
+        perror("xc_map_foreign_bulk");
+        exit(-1);
+    }
+
+    entry->vaddr_base = vaddr_base;
+    entry->paddr_index = address_index;
+
+    for (i = 0; i < nb_pfn; i += BITS_PER_LONG) {
+        unsigned long word = 0;
+        if ((i + BITS_PER_LONG) > nb_pfn) {
+            j = nb_pfn % BITS_PER_LONG;
+        } else {
+            j = BITS_PER_LONG;
+        }
+        while (j > 0) {
+            word = (word << 1) | !err[i + --j];
+        }
+        entry->valid_mapping[i / BITS_PER_LONG] = word;
+    }
+
+    qemu_free(pfns);
+    qemu_free(err);
+}
+
+uint8_t *qemu_map_cache(target_phys_addr_t phys_addr, target_phys_addr_t size, uint8_t lock)
+{
+    MapCacheEntry *entry, *pentry = NULL;
+    target_phys_addr_t address_index  = phys_addr >> MCACHE_BUCKET_SHIFT;
+    target_phys_addr_t address_offset = phys_addr & (MCACHE_BUCKET_SIZE - 1);
+
+    trace_qemu_map_cache(phys_addr);
+
+    if (address_index == mapcache->last_address_index && !lock) {
+        trace_qemu_map_cache_return(mapcache->last_address_vaddr + address_offset);
+        return mapcache->last_address_vaddr + address_offset;
+    }
+
+    entry = &mapcache->entry[address_index % mapcache->nr_buckets];
+
+    while (entry && entry->lock && entry->paddr_index != address_index && entry->vaddr_base) {
+        pentry = entry;
+        entry = entry->next;
+    }
+    if (!entry) {
+        entry = qemu_mallocz(sizeof (MapCacheEntry));
+        pentry->next = entry;
+        qemu_remap_bucket(entry, size ? : MCACHE_BUCKET_SIZE, address_index);
+    } else if (!entry->lock) {
+        if (!entry->vaddr_base || entry->paddr_index != address_index ||
+            !test_bit(address_offset >> XC_PAGE_SHIFT, entry->valid_mapping)) {
+            qemu_remap_bucket(entry, size ? : MCACHE_BUCKET_SIZE, address_index);
+        }
+    }
+
+    if (!test_bit(address_offset >> XC_PAGE_SHIFT, entry->valid_mapping)) {
+        mapcache->last_address_index = -1;
+        trace_qemu_map_cache_return(NULL);
+        return NULL;
+    }
+
+    mapcache->last_address_index = address_index;
+    mapcache->last_address_vaddr = entry->vaddr_base;
+    if (lock) {
+        MapCacheRev *reventry = qemu_mallocz(sizeof(MapCacheRev));
+        entry->lock++;
+        reventry->vaddr_req = mapcache->last_address_vaddr + address_offset;
+        reventry->paddr_index = mapcache->last_address_index;
+        QTAILQ_INSERT_HEAD(&mapcache->locked_entries, reventry, next);
+    }
+
+    trace_qemu_map_cache_return(mapcache->last_address_vaddr + address_offset);
+    return mapcache->last_address_vaddr + address_offset;
+}
+
+ram_addr_t qemu_ram_addr_from_mapcache(void *ptr)
+{
+    MapCacheRev *reventry;
+    target_phys_addr_t paddr_index;
+    int found = 0;
+
+    QTAILQ_FOREACH(reventry, &mapcache->locked_entries, next) {
+        if (reventry->vaddr_req == ptr) {
+            paddr_index = reventry->paddr_index;
+            found = 1;
+            break;
+        }
+    }
+    if (!found) {
+        fprintf(stderr, "qemu_ram_addr_from_mapcache, could not find %p\n", ptr);
+        QTAILQ_FOREACH(reventry, &mapcache->locked_entries, next) {
+            DPRINTF("   "TARGET_FMT_plx" -> %p is present\n", reventry->paddr_index,
+                    reventry->vaddr_req);
+        }
+        abort();
+        return 0;
+    }
+
+    return paddr_index << MCACHE_BUCKET_SHIFT;
+}
+
+void qemu_invalidate_entry(uint8_t *buffer)
+{
+    MapCacheEntry *entry = NULL, *pentry = NULL;
+    MapCacheRev *reventry;
+    target_phys_addr_t paddr_index;
+    int found = 0;
+
+    if (mapcache->last_address_vaddr == buffer) {
+        mapcache->last_address_index = -1;
+    }
+
+    QTAILQ_FOREACH(reventry, &mapcache->locked_entries, next) {
+        if (reventry->vaddr_req == buffer) {
+            paddr_index = reventry->paddr_index;
+            found = 1;
+            break;
+        }
+    }
+    if (!found) {
+        DPRINTF("qemu_invalidate_entry, could not find %p\n", buffer);
+        QTAILQ_FOREACH(reventry, &mapcache->locked_entries, next) {
+            DPRINTF("   "TARGET_FMT_plx" -> %p is present\n", reventry->paddr_index, reventry->vaddr_req);
+        }
+        return;
+    }
+    QTAILQ_REMOVE(&mapcache->locked_entries, reventry, next);
+    qemu_free(reventry);
+
+    entry = &mapcache->entry[paddr_index % mapcache->nr_buckets];
+    while (entry && entry->paddr_index != paddr_index) {
+        pentry = entry;
+        entry = entry->next;
+    }
+    if (!entry) {
+        DPRINTF("Trying to unmap address %p that is not in the mapcache!\n", buffer);
+        return;
+    }
+    entry->lock--;
+    if (entry->lock > 0 || pentry == NULL) {
+        return;
+    }
+
+    pentry->next = entry->next;
+    if (munmap(entry->vaddr_base, MCACHE_BUCKET_SIZE) != 0) {
+        perror("unmap fails");
+        exit(-1);
+    }
+    qemu_free(entry);
+}
+
+void qemu_invalidate_map_cache(void)
+{
+    unsigned long i;
+    MapCacheRev *reventry;
+
+    /* Flush pending AIO before destroying the mapcache */
+    qemu_aio_flush();
+
+    QTAILQ_FOREACH(reventry, &mapcache->locked_entries, next) {
+        DPRINTF("There should be no locked mappings at this time, "
+                "but "TARGET_FMT_plx" -> %p is present\n",
+                reventry->paddr_index, reventry->vaddr_req);
+    }
+
+    mapcache_lock();
+
+    for (i = 0; i < mapcache->nr_buckets; i++) {
+        MapCacheEntry *entry = &mapcache->entry[i];
+
+        if (entry->vaddr_base == NULL) {
+            continue;
+        }
+
+        if (munmap(entry->vaddr_base, MCACHE_BUCKET_SIZE) != 0) {
+            perror("unmap fails");
+            exit(-1);
+        }
+
+        entry->paddr_index = 0;
+        entry->vaddr_base = NULL;
+    }
+
+    mapcache->last_address_index = -1;
+    mapcache->last_address_vaddr = NULL;
+
+    mapcache_unlock();
+}
+
+uint8_t *xen_map_block(target_phys_addr_t phys_addr, target_phys_addr_t size)
+{
+    uint8_t *vaddr_base;
+    xen_pfn_t *pfns;
+    int *err;
+    unsigned int i;
+    target_phys_addr_t nb_pfn = size >> XC_PAGE_SHIFT;
+
+    trace_xen_map_block(phys_addr, size);
+    phys_addr >>= XC_PAGE_SHIFT;
+
+    pfns = qemu_mallocz(nb_pfn * sizeof (xen_pfn_t));
+    err = qemu_mallocz(nb_pfn * sizeof (int));
+
+    for (i = 0; i < nb_pfn; i++) {
+        pfns[i] = phys_addr + i;
+    }
+
+    vaddr_base = xc_map_foreign_bulk(xen_xc, xen_domid, PROT_READ|PROT_WRITE,
+                                     pfns, err, nb_pfn);
+    if (vaddr_base == NULL) {
+        perror("xc_map_foreign_bulk");
+        exit(-1);
+    }
+
+    qemu_free(pfns);
+    qemu_free(err);
+
+    return vaddr_base;
+}
diff --git a/xen-mapcache.h b/xen-mapcache.h
new file mode 100644
index 0000000..339444c
--- /dev/null
+++ b/xen-mapcache.h
@@ -0,0 +1,37 @@ 
+/*
+ * Copyright (C) 2011       Citrix Ltd.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#ifndef XEN_MAPCACHE_H
+#define XEN_MAPCACHE_H
+
+#include <sys/mman.h>
+#include "trace.h"
+
+void     qemu_map_cache_init(void);
+uint8_t  *qemu_map_cache(target_phys_addr_t phys_addr, target_phys_addr_t size, uint8_t lock);
+void     qemu_map_cache_unlock(void *phys_addr);
+ram_addr_t qemu_ram_addr_from_mapcache(void *ptr);
+void     qemu_invalidate_entry(uint8_t *buffer);
+void     qemu_invalidate_map_cache(void);
+
+uint8_t *xen_map_block(target_phys_addr_t phys_addr, target_phys_addr_t size);
+
+static inline void xen_unmap_block(void *addr, ram_addr_t size)
+{
+    trace_xen_unmap_block(addr, size);
+
+    if (munmap(addr, size) != 0) {
+        hw_error("xen_unmap_block: %s", strerror(errno));
+    }
+}
+
+
+#define mapcache_lock()   ((void)0)
+#define mapcache_unlock() ((void)0)
+
+#endif /* !XEN_MAPCACHE_H */
diff --git a/xen-stub.c b/xen-stub.c
index 3a8449c..8d2fa54 100644
--- a/xen-stub.c
+++ b/xen-stub.c
@@ -22,6 +22,10 @@  void xen_piix_pci_write_config_client(uint32_t address, uint32_t val, int len)
 {
 }
 
+void xen_ram_alloc(ram_addr_t ram_addr, ram_addr_t size)
+{
+}
+
 qemu_irq *xen_interrupt_controller_init(void)
 {
     return NULL;