kvmvapic: Introduce TPR access optimization for Windows guests

This enables acceleration for MMIO-based TPR registers accesses of
32-bit Windows guest systems. It is mostly useful with KVM enabled,
either on older Intel CPUs (without flexpriority feature, can also be
manually disabled for testing) or any current AMD processor.

The approach introduced here is derived from the original version of
qemu-kvm. It was refactored, documented, and extended by support for
user space APIC emulation, both with and without KVM acceleration. The
VMState format was kept compatible, so was the ABI to the option ROM
that implements the guest-side para-virtualized driver service. This
enables seamless migration from qemu-kvm to upstream or, one day,
between KVM and TCG mode.

The basic concept goes like this:
 - VAPIC PV interface consisting of I/O port 0x7e and (for KVM in-kernel
   irqchip) a vmcall hypercall is registered
 - VAPIC option ROM is loaded into guest
 - option ROM activates TPR MMIO access reporting via port 0x7e
 - TPR accesses are trapped and patched in the guest to call into option
   ROM instead, VAPIC support is enabled
 - option ROM TPR helpers track state in memory and invoke hypercall to
   poll for pending IRQs if required

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

5 files changed, 1041 insertions, 13 deletions

diff --git a/hw/apic.c b/hw/apic.c
index ff9d24e914..4eeaf8801c 100644
--- a/hw/apic.c
+++ b/hw/apic.c
@@ -35,6 +35,10 @@
 #define MSI_ADDR_DEST_ID_SHIFT		12
 #define	MSI_ADDR_DEST_ID_MASK		0x00ffff0
 
+#define SYNC_FROM_VAPIC                 0x1
+#define SYNC_TO_VAPIC                   0x2
+#define SYNC_ISR_IRR_TO_VAPIC           0x4
+
 static APICCommonState *local_apics[MAX_APICS + 1];
 
 static void apic_set_irq(APICCommonState *s, int vector_num, int trigger_mode);
@@ -78,6 +82,70 @@ static inline int get_bit(uint32_t *tab, int index)
     return !!(tab[i] & mask);
 }
 
+/* return -1 if no bit is set */
+static int get_highest_priority_int(uint32_t *tab)
+{
+    int i;
+    for (i = 7; i >= 0; i--) {
+        if (tab[i] != 0) {
+            return i * 32 + fls_bit(tab[i]);
+        }
+    }
+    return -1;
+}
+
+static void apic_sync_vapic(APICCommonState *s, int sync_type)
+{
+    VAPICState vapic_state;
+    size_t length;
+    off_t start;
+    int vector;
+
+    if (!s->vapic_paddr) {
+        return;
+    }
+    if (sync_type & SYNC_FROM_VAPIC) {
+        cpu_physical_memory_rw(s->vapic_paddr, (void *)&vapic_state,
+                               sizeof(vapic_state), 0);
+        s->tpr = vapic_state.tpr;
+    }
+    if (sync_type & (SYNC_TO_VAPIC | SYNC_ISR_IRR_TO_VAPIC)) {
+        start = offsetof(VAPICState, isr);
+        length = offsetof(VAPICState, enabled) - offsetof(VAPICState, isr);
+
+        if (sync_type & SYNC_TO_VAPIC) {
+            assert(qemu_cpu_is_self(s->cpu_env));
+
+            vapic_state.tpr = s->tpr;
+            vapic_state.enabled = 1;
+            start = 0;
+            length = sizeof(VAPICState);
+        }
+
+        vector = get_highest_priority_int(s->isr);
+        if (vector < 0) {
+            vector = 0;
+        }
+        vapic_state.isr = vector & 0xf0;
+
+        vapic_state.zero = 0;
+
+        vector = get_highest_priority_int(s->irr);
+        if (vector < 0) {
+            vector = 0;
+        }
+        vapic_state.irr = vector & 0xff;
+
+        cpu_physical_memory_write_rom(s->vapic_paddr + start,
+                                      ((void *)&vapic_state) + start, length);
+    }
+}
+
+static void apic_vapic_base_update(APICCommonState *s)
+{
+    apic_sync_vapic(s, SYNC_TO_VAPIC);
+}
+
 static void apic_local_deliver(APICCommonState *s, int vector)
 {
     uint32_t lvt = s->lvt[vector];
@@ -239,20 +307,17 @@ static void apic_set_base(APICCommonState *s, uint64_t val)
 
 static void apic_set_tpr(APICCommonState *s, uint8_t val)
 {
-    s->tpr = (val & 0x0f) << 4;
-    apic_update_irq(s);
+    /* Updates from cr8 are ignored while the VAPIC is active */
+    if (!s->vapic_paddr) {
+        s->tpr = val << 4;
+        apic_update_irq(s);
+    }
 }
 
-/* return -1 if no bit is set */
-static int get_highest_priority_int(uint32_t *tab)
+static uint8_t apic_get_tpr(APICCommonState *s)
 {
-    int i;
-    for(i = 7; i >= 0; i--) {
-        if (tab[i] != 0) {
-            return i * 32 + fls_bit(tab[i]);
-        }
-    }
-    return -1;
+    apic_sync_vapic(s, SYNC_FROM_VAPIC);
+    return s->tpr >> 4;
 }
 
 static int apic_get_ppr(APICCommonState *s)
@@ -312,6 +377,14 @@ static void apic_update_irq(APICCommonState *s)
     }
 }
 
+void apic_poll_irq(DeviceState *d)
+{
+    APICCommonState *s = APIC_COMMON(d);
+
+    apic_sync_vapic(s, SYNC_FROM_VAPIC);
+    apic_update_irq(s);
+}
+
 static void apic_set_irq(APICCommonState *s, int vector_num, int trigger_mode)
 {
     apic_report_irq_delivered(!get_bit(s->irr, vector_num));
@@ -321,6 +394,16 @@ static void apic_set_irq(APICCommonState *s, int vector_num, int trigger_mode)
         set_bit(s->tmr, vector_num);
     else
         reset_bit(s->tmr, vector_num);
+    if (s->vapic_paddr) {
+        apic_sync_vapic(s, SYNC_ISR_IRR_TO_VAPIC);
+        /*
+         * The vcpu thread needs to see the new IRR before we pull its current
+         * TPR value. That way, if we miss a lowering of the TRP, the guest
+         * has the chance to notice the new IRR and poll for IRQs on its own.
+         */
+        smp_wmb();
+        apic_sync_vapic(s, SYNC_FROM_VAPIC);
+    }
     apic_update_irq(s);
 }
 
@@ -334,6 +417,7 @@ static void apic_eoi(APICCommonState *s)
     if (!(s->spurious_vec & APIC_SV_DIRECTED_IO) && get_bit(s->tmr, isrv)) {
         ioapic_eoi_broadcast(isrv);
     }
+    apic_sync_vapic(s, SYNC_FROM_VAPIC | SYNC_TO_VAPIC);
     apic_update_irq(s);
 }
 
@@ -471,15 +555,19 @@ int apic_get_interrupt(DeviceState *d)
     if (!(s->spurious_vec & APIC_SV_ENABLE))
         return -1;
 
+    apic_sync_vapic(s, SYNC_FROM_VAPIC);
     intno = apic_irq_pending(s);
 
     if (intno == 0) {
+        apic_sync_vapic(s, SYNC_TO_VAPIC);
         return -1;
     } else if (intno < 0) {
+        apic_sync_vapic(s, SYNC_TO_VAPIC);
         return s->spurious_vec & 0xff;
     }
     reset_bit(s->irr, intno);
     set_bit(s->isr, intno);
+    apic_sync_vapic(s, SYNC_TO_VAPIC);
     apic_update_irq(s);
     return intno;
 }
@@ -576,6 +664,10 @@ static uint32_t apic_mem_readl(void *opaque, target_phys_addr_t addr)
         val = 0x11 | ((APIC_LVT_NB - 1) << 16); /* version 0x11 */
         break;
     case 0x08:
+        apic_sync_vapic(s, SYNC_FROM_VAPIC);
+        if (apic_report_tpr_access) {
+            cpu_report_tpr_access(s->cpu_env, TPR_ACCESS_READ);
+        }
         val = s->tpr;
         break;
     case 0x09:
@@ -675,7 +767,11 @@ static void apic_mem_writel(void *opaque, target_phys_addr_t addr, uint32_t val)
     case 0x03:
         break;
     case 0x08:
+        if (apic_report_tpr_access) {
+            cpu_report_tpr_access(s->cpu_env, TPR_ACCESS_WRITE);
+        }
         s->tpr = val;
+        apic_sync_vapic(s, SYNC_TO_VAPIC);
         apic_update_irq(s);
         break;
     case 0x09:
@@ -737,6 +833,11 @@ static void apic_mem_writel(void *opaque, target_phys_addr_t addr, uint32_t val)
     }
 }
 
+static void apic_pre_save(APICCommonState *s)
+{
+    apic_sync_vapic(s, SYNC_FROM_VAPIC);
+}
+
 static void apic_post_load(APICCommonState *s)
 {
     if (s->timer_expiry != -1) {
@@ -770,7 +871,10 @@ static void apic_class_init(ObjectClass *klass, void *data)
     k->init = apic_init;
     k->set_base = apic_set_base;
     k->set_tpr = apic_set_tpr;
+    k->get_tpr = apic_get_tpr;
+    k->vapic_base_update = apic_vapic_base_update;
     k->external_nmi = apic_external_nmi;
+    k->pre_save = apic_pre_save;
     k->post_load = apic_post_load;
 }
 
diff --git a/hw/apic_common.c b/hw/apic_common.c
index 340d793c70..60b82596e7 100644
--- a/hw/apic_common.c
+++ b/hw/apic_common.c
@@ -20,8 +20,10 @@
 #include "apic.h"
 #include "apic_internal.h"
 #include "trace.h"
+#include "kvm.h"
 
 static int apic_irq_delivered;
+bool apic_report_tpr_access;
 
 void cpu_set_apic_base(DeviceState *d, uint64_t val)
 {
@@ -63,14 +65,45 @@ void cpu_set_apic_tpr(DeviceState *d, uint8_t val)
 
 uint8_t cpu_get_apic_tpr(DeviceState *d)
 {
+    APICCommonState *s;
+    APICCommonClass *info;
+
+    if (!d) {
+        return 0;
+    }
+
+    s = APIC_COMMON(d);
+    info = APIC_COMMON_GET_CLASS(s);
+
+    return info->get_tpr(s);
+}
+
+void apic_enable_tpr_access_reporting(DeviceState *d, bool enable)
+{
+    APICCommonState *s = DO_UPCAST(APICCommonState, busdev.qdev, d);
+    APICCommonClass *info = APIC_COMMON_GET_CLASS(s);
+
+    apic_report_tpr_access = enable;
+    if (info->enable_tpr_reporting) {
+        info->enable_tpr_reporting(s, enable);
+    }
+}
+
+void apic_enable_vapic(DeviceState *d, target_phys_addr_t paddr)
+{
     APICCommonState *s = DO_UPCAST(APICCommonState, busdev.qdev, d);
+    APICCommonClass *info = APIC_COMMON_GET_CLASS(s);
 
-    return s ? s->tpr >> 4 : 0;
+    s->vapic_paddr = paddr;
+    info->vapic_base_update(s);
 }
 
 void apic_handle_tpr_access_report(DeviceState *d, target_ulong ip,
                                    TPRAccess access)
 {
+    APICCommonState *s = DO_UPCAST(APICCommonState, busdev.qdev, d);
+
+    vapic_report_tpr_access(s->vapic, s->cpu_env, ip, access);
 }
 
 void apic_report_irq_delivered(int delivered)
@@ -171,12 +204,16 @@ void apic_init_reset(DeviceState *d)
 static void apic_reset_common(DeviceState *d)
 {
     APICCommonState *s = DO_UPCAST(APICCommonState, busdev.qdev, d);
+    APICCommonClass *info = APIC_COMMON_GET_CLASS(s);
     bool bsp;
 
     bsp = cpu_is_bsp(s->cpu_env);
     s->apicbase = 0xfee00000 |
         (bsp ? MSR_IA32_APICBASE_BSP : 0) | MSR_IA32_APICBASE_ENABLE;
 
+    s->vapic_paddr = 0;
+    info->vapic_base_update(s);
+
     apic_init_reset(d);
 
     if (bsp) {
@@ -239,6 +276,7 @@ static int apic_init_common(SysBusDevice *dev)
 {
     APICCommonState *s = APIC_COMMON(dev);
     APICCommonClass *info;
+    static DeviceState *vapic;
     static int apic_no;
 
     if (apic_no >= MAX_APICS) {
@@ -249,10 +287,29 @@ static int apic_init_common(SysBusDevice *dev)
     info = APIC_COMMON_GET_CLASS(s);
     info->init(s);
 
-    sysbus_init_mmio(&s->busdev, &s->io_memory);
+    sysbus_init_mmio(dev, &s->io_memory);
+
+    if (!vapic && s->vapic_control & VAPIC_ENABLE_MASK) {
+        vapic = sysbus_create_simple("kvmvapic", -1, NULL);
+    }
+    s->vapic = vapic;
+    if (apic_report_tpr_access && info->enable_tpr_reporting) {
+        info->enable_tpr_reporting(s, true);
+    }
+
     return 0;
 }
 
+static void apic_dispatch_pre_save(void *opaque)
+{
+    APICCommonState *s = APIC_COMMON(opaque);
+    APICCommonClass *info = APIC_COMMON_GET_CLASS(s);
+
+    if (info->pre_save) {
+        info->pre_save(s);
+    }
+}
+
 static int apic_dispatch_post_load(void *opaque, int version_id)
 {
     APICCommonState *s = APIC_COMMON(opaque);
@@ -270,6 +327,7 @@ static const VMStateDescription vmstate_apic_common = {
     .minimum_version_id = 3,
     .minimum_version_id_old = 1,
     .load_state_old = apic_load_old,
+    .pre_save = apic_dispatch_pre_save,
     .post_load = apic_dispatch_post_load,
     .fields = (VMStateField[]) {
         VMSTATE_UINT32(apicbase, APICCommonState),
@@ -299,6 +357,8 @@ static const VMStateDescription vmstate_apic_common = {
 static Property apic_properties_common[] = {
     DEFINE_PROP_UINT8("id", APICCommonState, id, -1),
     DEFINE_PROP_PTR("cpu_env", APICCommonState, cpu_env),
+    DEFINE_PROP_BIT("vapic", APICCommonState, vapic_control, VAPIC_ENABLE_BIT,
+                    true),
     DEFINE_PROP_END_OF_LIST(),
 };
 
diff --git a/hw/apic_internal.h b/hw/apic_internal.h
index 0cab010717..60a6a8bdae 100644
--- a/hw/apic_internal.h
+++ b/hw/apic_internal.h
@@ -61,6 +61,9 @@
 #define APIC_SV_DIRECTED_IO             (1<<12)
 #define APIC_SV_ENABLE                  (1<<8)
 
+#define VAPIC_ENABLE_BIT                0
+#define VAPIC_ENABLE_MASK               (1 << VAPIC_ENABLE_BIT)
+
 #define MAX_APICS 255
 
 #define MSI_SPACE_SIZE                  0x100000
@@ -82,7 +85,11 @@ typedef struct APICCommonClass
     void (*init)(APICCommonState *s);
     void (*set_base)(APICCommonState *s, uint64_t val);
     void (*set_tpr)(APICCommonState *s, uint8_t val);
+    uint8_t (*get_tpr)(APICCommonState *s);
+    void (*enable_tpr_reporting)(APICCommonState *s, bool enable);
+    void (*vapic_base_update)(APICCommonState *s);
     void (*external_nmi)(APICCommonState *s);
+    void (*pre_save)(APICCommonState *s);
     void (*post_load)(APICCommonState *s);
 } APICCommonClass;
 
@@ -114,9 +121,29 @@ struct APICCommonState {
     int64_t timer_expiry;
     int sipi_vector;
     int wait_for_sipi;
+
+    uint32_t vapic_control;
+    DeviceState *vapic;
+    target_phys_addr_t vapic_paddr; /* note: persistence via kvmvapic */
 };
 
+typedef struct VAPICState {
+    uint8_t tpr;
+    uint8_t isr;
+    uint8_t zero;
+    uint8_t irr;
+    uint8_t enabled;
+} QEMU_PACKED VAPICState;
+
+extern bool apic_report_tpr_access;
+
 void apic_report_irq_delivered(int delivered);
 bool apic_next_timer(APICCommonState *s, int64_t current_time);
+void apic_enable_tpr_access_reporting(DeviceState *d, bool enable);
+void apic_enable_vapic(DeviceState *d, target_phys_addr_t paddr);
+void apic_poll_irq(DeviceState *d);
+
+void vapic_report_tpr_access(DeviceState *dev, void *cpu, target_ulong ip,
+                             TPRAccess access);
 
 #endif /* !QEMU_APIC_INTERNAL_H */
diff --git a/hw/kvm/apic.c b/hw/kvm/apic.c
index 5bb0a4b9fd..9ca68f81aa 100644
--- a/hw/kvm/apic.c
+++ b/hw/kvm/apic.c
@@ -92,6 +92,35 @@ static void kvm_apic_set_tpr(APICCommonState *s, uint8_t val)
     s->tpr = (val & 0x0f) << 4;
 }
 
+static uint8_t kvm_apic_get_tpr(APICCommonState *s)
+{
+    return s->tpr >> 4;
+}
+
+static void kvm_apic_enable_tpr_reporting(APICCommonState *s, bool enable)
+{
+    struct kvm_tpr_access_ctl ctl = {
+        .enabled = enable
+    };
+
+    kvm_vcpu_ioctl(s->cpu_env, KVM_TPR_ACCESS_REPORTING, &ctl);
+}
+
+static void kvm_apic_vapic_base_update(APICCommonState *s)
+{
+    struct kvm_vapic_addr vapid_addr = {
+        .vapic_addr = s->vapic_paddr,
+    };
+    int ret;
+
+    ret = kvm_vcpu_ioctl(s->cpu_env, KVM_SET_VAPIC_ADDR, &vapid_addr);
+    if (ret < 0) {
+        fprintf(stderr, "KVM: setting VAPIC address failed (%s)\n",
+                strerror(-ret));
+        abort();
+    }
+}
+
 static void do_inject_external_nmi(void *data)
 {
     APICCommonState *s = data;
@@ -129,6 +158,9 @@ static void kvm_apic_class_init(ObjectClass *klass, void *data)
     k->init = kvm_apic_init;
     k->set_base = kvm_apic_set_base;
     k->set_tpr = kvm_apic_set_tpr;
+    k->get_tpr = kvm_apic_get_tpr;
+    k->enable_tpr_reporting = kvm_apic_enable_tpr_reporting;
+    k->vapic_base_update = kvm_apic_vapic_base_update;
     k->external_nmi = kvm_apic_external_nmi;
 }
 
diff --git a/hw/kvmvapic.c b/hw/kvmvapic.c
new file mode 100644
index 0000000000..36ccfbcdbd
--- /dev/null
+++ b/hw/kvmvapic.c
@@ -0,0 +1,805 @@
+/*
+ * TPR optimization for 32-bit Windows guests (XP and Server 2003)
+ *
+ * Copyright (C) 2007-2008 Qumranet Technologies
+ * Copyright (C) 2012      Jan Kiszka, Siemens AG
+ *
+ * This work is licensed under the terms of the GNU GPL version 2, or
+ * (at your option) any later version. See the COPYING file in the
+ * top-level directory.
+ */
+#include "sysemu.h"
+#include "cpus.h"
+#include "kvm.h"
+#include "apic_internal.h"
+
+#define APIC_DEFAULT_ADDRESS    0xfee00000
+
+#define VAPIC_IO_PORT           0x7e
+
+#define VAPIC_CPU_SHIFT         7
+
+#define ROM_BLOCK_SIZE          512
+#define ROM_BLOCK_MASK          (~(ROM_BLOCK_SIZE - 1))
+
+typedef enum VAPICMode {
+    VAPIC_INACTIVE = 0,
+    VAPIC_ACTIVE   = 1,
+    VAPIC_STANDBY  = 2,
+} VAPICMode;
+
+typedef struct VAPICHandlers {
+    uint32_t set_tpr;
+    uint32_t set_tpr_eax;
+    uint32_t get_tpr[8];
+    uint32_t get_tpr_stack;
+} QEMU_PACKED VAPICHandlers;
+
+typedef struct GuestROMState {
+    char signature[8];
+    uint32_t vaddr;
+    uint32_t fixup_start;
+    uint32_t fixup_end;
+    uint32_t vapic_vaddr;
+    uint32_t vapic_size;
+    uint32_t vcpu_shift;
+    uint32_t real_tpr_addr;
+    VAPICHandlers up;
+    VAPICHandlers mp;
+} QEMU_PACKED GuestROMState;
+
+typedef struct VAPICROMState {
+    SysBusDevice busdev;
+    MemoryRegion io;
+    MemoryRegion rom;
+    uint32_t state;
+    uint32_t rom_state_paddr;
+    uint32_t rom_state_vaddr;
+    uint32_t vapic_paddr;
+    uint32_t real_tpr_addr;
+    GuestROMState rom_state;
+    size_t rom_size;
+    bool rom_mapped_writable;
+} VAPICROMState;
+
+#define TPR_INSTR_ABS_MODRM             0x1
+#define TPR_INSTR_MATCH_MODRM_REG       0x2
+
+typedef struct TPRInstruction {
+    uint8_t opcode;
+    uint8_t modrm_reg;
+    unsigned int flags;
+    TPRAccess access;
+    size_t length;
+    off_t addr_offset;
+} TPRInstruction;
+
+/* must be sorted by length, shortest first */
+static const TPRInstruction tpr_instr[] = {
+    { /* mov abs to eax */
+        .opcode = 0xa1,
+        .access = TPR_ACCESS_READ,
+        .length = 5,
+        .addr_offset = 1,
+    },
+    { /* mov eax to abs */
+        .opcode = 0xa3,
+        .access = TPR_ACCESS_WRITE,
+        .length = 5,
+        .addr_offset = 1,
+    },
+    { /* mov r32 to r/m32 */
+        .opcode = 0x89,
+        .flags = TPR_INSTR_ABS_MODRM,
+        .access = TPR_ACCESS_WRITE,
+        .length = 6,
+        .addr_offset = 2,
+    },
+    { /* mov r/m32 to r32 */
+        .opcode = 0x8b,
+        .flags = TPR_INSTR_ABS_MODRM,
+        .access = TPR_ACCESS_READ,
+        .length = 6,
+        .addr_offset = 2,
+    },
+    { /* push r/m32 */
+        .opcode = 0xff,
+        .modrm_reg = 6,
+        .flags = TPR_INSTR_ABS_MODRM | TPR_INSTR_MATCH_MODRM_REG,
+        .access = TPR_ACCESS_READ,
+        .length = 6,
+        .addr_offset = 2,
+    },
+    { /* mov imm32, r/m32 (c7/0) */
+        .opcode = 0xc7,
+        .modrm_reg = 0,
+        .flags = TPR_INSTR_ABS_MODRM | TPR_INSTR_MATCH_MODRM_REG,
+        .access = TPR_ACCESS_WRITE,
+        .length = 10,
+        .addr_offset = 2,
+    },
+};
+
+static void read_guest_rom_state(VAPICROMState *s)
+{
+    cpu_physical_memory_rw(s->rom_state_paddr, (void *)&s->rom_state,
+                           sizeof(GuestROMState), 0);
+}
+
+static void write_guest_rom_state(VAPICROMState *s)
+{
+    cpu_physical_memory_rw(s->rom_state_paddr, (void *)&s->rom_state,
+                           sizeof(GuestROMState), 1);
+}
+
+static void update_guest_rom_state(VAPICROMState *s)
+{
+    read_guest_rom_state(s);
+
+    s->rom_state.real_tpr_addr = cpu_to_le32(s->real_tpr_addr);
+    s->rom_state.vcpu_shift = cpu_to_le32(VAPIC_CPU_SHIFT);
+
+    write_guest_rom_state(s);
+}
+
+static int find_real_tpr_addr(VAPICROMState *s, CPUState *env)
+{
+    target_phys_addr_t paddr;
+    target_ulong addr;
+
+    if (s->state == VAPIC_ACTIVE) {
+        return 0;
+    }
+    /*
+     * If there is no prior TPR access instruction we could analyze (which is
+     * the case after resume from hibernation), we need to scan the possible
+     * virtual address space for the APIC mapping.
+     */
+    for (addr = 0xfffff000; addr >= 0x80000000; addr -= TARGET_PAGE_SIZE) {
+        paddr = cpu_get_phys_page_debug(env, addr);
+        if (paddr != APIC_DEFAULT_ADDRESS) {
+            continue;
+        }
+        s->real_tpr_addr = addr + 0x80;
+        update_guest_rom_state(s);
+        return 0;
+    }
+    return -1;
+}
+
+static uint8_t modrm_reg(uint8_t modrm)
+{
+    return (modrm >> 3) & 7;
+}
+
+static bool is_abs_modrm(uint8_t modrm)
+{
+    return (modrm & 0xc7) == 0x05;
+}
+
+static bool opcode_matches(uint8_t *opcode, const TPRInstruction *instr)
+{
+    return opcode[0] == instr->opcode &&
+        (!(instr->flags & TPR_INSTR_ABS_MODRM) || is_abs_modrm(opcode[1])) &&
+        (!(instr->flags & TPR_INSTR_MATCH_MODRM_REG) ||
+         modrm_reg(opcode[1]) == instr->modrm_reg);
+}
+
+static int evaluate_tpr_instruction(VAPICROMState *s, CPUState *env,
+                                    target_ulong *pip, TPRAccess access)
+{
+    const TPRInstruction *instr;
+    target_ulong ip = *pip;
+    uint8_t opcode[2];
+    uint32_t real_tpr_addr;
+    int i;
+
+    if ((ip & 0xf0000000ULL) != 0x80000000ULL &&
+        (ip & 0xf0000000ULL) != 0xe0000000ULL) {
+        return -1;
+    }
+
+    /*
+     * Early Windows 2003 SMP initialization contains a
+     *
+     *   mov imm32, r/m32
+     *
+     * instruction that is patched by TPR optimization. The problem is that
+     * RSP, used by the patched instruction, is zero, so the guest gets a
+     * double fault and dies.
+     */
+    if (env->regs[R_ESP] == 0) {
+        return -1;
+    }
+
+    if (kvm_enabled() && !kvm_irqchip_in_kernel()) {
+        /*
+         * KVM without kernel-based TPR access reporting will pass an IP that
+         * points after the accessing instruction. So we need to look backward
+         * to find the reason.
+         */
+        for (i = 0; i < ARRAY_SIZE(tpr_instr); i++) {
+            instr = &tpr_instr[i];
+            if (instr->access != access) {
+                continue;
+            }
+            if (cpu_memory_rw_debug(env, ip - instr->length, opcode,
+                                    sizeof(opcode), 0) < 0) {
+                return -1;
+            }
+            if (opcode_matches(opcode, instr)) {
+                ip -= instr->length;
+                goto instruction_ok;
+            }
+        }
+        return -1;
+    } else {
+        if (cpu_memory_rw_debug(env, ip, opcode, sizeof(opcode), 0) < 0) {
+            return -1;
+        }
+        for (i = 0; i < ARRAY_SIZE(tpr_instr); i++) {
+            instr = &tpr_instr[i];
+            if (opcode_matches(opcode, instr)) {
+                goto instruction_ok;
+            }
+        }
+        return -1;
+    }
+
+instruction_ok:
+    /*
+     * Grab the virtual TPR address from the instruction
+     * and update the cached values.
+     */
+    if (cpu_memory_rw_debug(env, ip + instr->addr_offset,
+                            (void *)&real_tpr_addr,
+                            sizeof(real_tpr_addr), 0) < 0) {
+        return -1;
+    }
+    real_tpr_addr = le32_to_cpu(real_tpr_addr);
+    if ((real_tpr_addr & 0xfff) != 0x80) {
+        return -1;
+    }
+    s->real_tpr_addr = real_tpr_addr;
+    update_guest_rom_state(s);
+
+    *pip = ip;
+    return 0;
+}
+
+static int update_rom_mapping(VAPICROMState *s, CPUState *env, target_ulong ip)
+{
+    target_phys_addr_t paddr;
+    uint32_t rom_state_vaddr;
+    uint32_t pos, patch, offset;
+
+    /* nothing to do if already activated */
+    if (s->state == VAPIC_ACTIVE) {
+        return 0;
+    }
+
+    /* bail out if ROM init code was not executed (missing ROM?) */
+    if (s->state == VAPIC_INACTIVE) {
+        return -1;
+    }
+
+    /* find out virtual address of the ROM */
+    rom_state_vaddr = s->rom_state_paddr + (ip & 0xf0000000);
+    paddr = cpu_get_phys_page_debug(env, rom_state_vaddr);
+    if (paddr == -1) {
+        return -1;
+    }
+    paddr += rom_state_vaddr & ~TARGET_PAGE_MASK;
+    if (paddr != s->rom_state_paddr) {
+        return -1;
+    }
+    read_guest_rom_state(s);
+    if (memcmp(s->rom_state.signature, "kvm aPiC", 8) != 0) {
+        return -1;
+    }
+    s->rom_state_vaddr = rom_state_vaddr;
+
+    /* fixup addresses in ROM if needed */
+    if (rom_state_vaddr == le32_to_cpu(s->rom_state.vaddr)) {
+        return 0;
+    }
+    for (pos = le32_to_cpu(s->rom_state.fixup_start);
+         pos < le32_to_cpu(s->rom_state.fixup_end);
+         pos += 4) {
+        cpu_physical_memory_rw(paddr + pos - s->rom_state.vaddr,
+                               (void *)&offset, sizeof(offset), 0);
+        offset = le32_to_cpu(offset);
+        cpu_physical_memory_rw(paddr + offset, (void *)&patch,
+                               sizeof(patch), 0);
+        patch = le32_to_cpu(patch);
+        patch += rom_state_vaddr - le32_to_cpu(s->rom_state.vaddr);
+        patch = cpu_to_le32(patch);
+        cpu_physical_memory_rw(paddr + offset, (void *)&patch,
+                               sizeof(patch), 1);
+    }
+    read_guest_rom_state(s);
+    s->vapic_paddr = paddr + le32_to_cpu(s->rom_state.vapic_vaddr) -
+        le32_to_cpu(s->rom_state.vaddr);
+
+    return 0;
+}
+
+/*
+ * Tries to read the unique processor number from the Kernel Processor Control
+ * Region (KPCR) of 32-bit Windows XP and Server 2003. Returns -1 if the KPCR
+ * cannot be accessed or is considered invalid. This also ensures that we are
+ * not patching the wrong guest.
+ */
+static int get_kpcr_number(CPUState *env)
+{
+    struct kpcr {
+        uint8_t  fill1[0x1c];
+        uint32_t self;
+        uint8_t  fill2[0x31];
+        uint8_t  number;
+    } QEMU_PACKED kpcr;
+
+    if (cpu_memory_rw_debug(env, env->segs[R_FS].base,
+                            (void *)&kpcr, sizeof(kpcr), 0) < 0 ||
+        kpcr.self != env->segs[R_FS].base) {
+        return -1;
+    }
+    return kpcr.number;
+}
+
+static int vapic_enable(VAPICROMState *s, CPUState *env)
+{
+    int cpu_number = get_kpcr_number(env);
+    target_phys_addr_t vapic_paddr;
+    static const uint8_t enabled = 1;
+
+    if (cpu_number < 0) {
+        return -1;
+    }
+    vapic_paddr = s->vapic_paddr +
+        (((target_phys_addr_t)cpu_number) << VAPIC_CPU_SHIFT);
+    cpu_physical_memory_rw(vapic_paddr + offsetof(VAPICState, enabled),
+                           (void *)&enabled, sizeof(enabled), 1);
+    apic_enable_vapic(env->apic_state, vapic_paddr);
+
+    s->state = VAPIC_ACTIVE;
+
+    return 0;
+}
+
+static void patch_byte(CPUState *env, target_ulong addr, uint8_t byte)
+{
+    cpu_memory_rw_debug(env, addr, &byte, 1, 1);
+}
+
+static void patch_call(VAPICROMState *s, CPUState *env, target_ulong ip,
+                       uint32_t target)
+{
+    uint32_t offset;
+
+    offset = cpu_to_le32(target - ip - 5);
+    patch_byte(env, ip, 0xe8); /* call near */
+    cpu_memory_rw_debug(env, ip + 1, (void *)&offset, sizeof(offset), 1);
+}
+
+static void patch_instruction(VAPICROMState *s, CPUState *env, target_ulong ip)
+{
+    target_phys_addr_t paddr;
+    VAPICHandlers *handlers;
+    uint8_t opcode[2];
+    uint32_t imm32;
+
+    if (smp_cpus == 1) {
+        handlers = &s->rom_state.up;
+    } else {
+        handlers = &s->rom_state.mp;
+    }
+
+    pause_all_vcpus();
+
+    cpu_memory_rw_debug(env, ip, opcode, sizeof(opcode), 0);
+
+    switch (opcode[0]) {
+    case 0x89: /* mov r32 to r/m32 */
+        patch_byte(env, ip, 0x50 + modrm_reg(opcode[1]));  /* push reg */
+        patch_call(s, env, ip + 1, handlers->set_tpr);
+        break;
+    case 0x8b: /* mov r/m32 to r32 */
+        patch_byte(env, ip, 0x90);
+        patch_call(s, env, ip + 1, handlers->get_tpr[modrm_reg(opcode[1])]);
+        break;
+    case 0xa1: /* mov abs to eax */
+        patch_call(s, env, ip, handlers->get_tpr[0]);
+        break;
+    case 0xa3: /* mov eax to abs */
+        patch_call(s, env, ip, handlers->set_tpr_eax);
+        break;
+    case 0xc7: /* mov imm32, r/m32 (c7/0) */
+        patch_byte(env, ip, 0x68);  /* push imm32 */
+        cpu_memory_rw_debug(env, ip + 6, (void *)&imm32, sizeof(imm32), 0);
+        cpu_memory_rw_debug(env, ip + 1, (void *)&imm32, sizeof(imm32), 1);
+        patch_call(s, env, ip + 5, handlers->set_tpr);
+        break;
+    case 0xff: /* push r/m32 */
+        patch_byte(env, ip, 0x50); /* push eax */
+        patch_call(s, env, ip + 1, handlers->get_tpr_stack);
+        break;
+    default:
+        abort();
+    }
+
+    resume_all_vcpus();
+
+    paddr = cpu_get_phys_page_debug(env, ip);
+    paddr += ip & ~TARGET_PAGE_MASK;
+    tb_invalidate_phys_page_range(paddr, paddr + 1, 1);
+}
+
+void vapic_report_tpr_access(DeviceState *dev, void *cpu, target_ulong ip,
+                             TPRAccess access)
+{
+    VAPICROMState *s = DO_UPCAST(VAPICROMState, busdev.qdev, dev);
+    CPUState *env = cpu;
+
+    cpu_synchronize_state(env);
+
+    if (evaluate_tpr_instruction(s, env, &ip, access) < 0) {
+        if (s->state == VAPIC_ACTIVE) {
+            vapic_enable(s, env);
+        }
+        return;
+    }
+    if (update_rom_mapping(s, env, ip) < 0) {
+        return;
+    }
+    if (vapic_enable(s, env) < 0) {
+        return;
+    }
+    patch_instruction(s, env, ip);
+}
+
+typedef struct VAPICEnableTPRReporting {
+    DeviceState *apic;
+    bool enable;
+} VAPICEnableTPRReporting;
+
+static void vapic_do_enable_tpr_reporting(void *data)
+{
+    VAPICEnableTPRReporting *info = data;
+
+    apic_enable_tpr_access_reporting(info->apic, info->enable);
+}
+
+static void vapic_enable_tpr_reporting(bool enable)
+{
+    VAPICEnableTPRReporting info = {
+        .enable = enable,
+    };
+    CPUState *env;
+
+    for (env = first_cpu; env != NULL; env = env->next_cpu) {
+        info.apic = env->apic_state;
+        run_on_cpu(env, vapic_do_enable_tpr_reporting, &info);
+    }
+}
+
+static void vapic_reset(DeviceState *dev)
+{
+    VAPICROMState *s = DO_UPCAST(VAPICROMState, busdev.qdev, dev);
+
+    if (s->state == VAPIC_ACTIVE) {
+        s->state = VAPIC_STANDBY;
+    }
+    vapic_enable_tpr_reporting(false);
+}
+
+/*
+ * Set the IRQ polling hypercalls to the supported variant:
+ *  - vmcall if using KVM in-kernel irqchip
+ *  - 32-bit VAPIC port write otherwise
+ */
+static int patch_hypercalls(VAPICROMState *s)
+{
+    target_phys_addr_t rom_paddr = s->rom_state_paddr & ROM_BLOCK_MASK;
+    static const uint8_t vmcall_pattern[] = { /* vmcall */
+        0xb8, 0x1, 0, 0, 0, 0xf, 0x1, 0xc1
+    };
+    static const uint8_t outl_pattern[] = { /* nop; outl %eax,0x7e */
+        0xb8, 0x1, 0, 0, 0, 0x90, 0xe7, 0x7e
+    };
+    uint8_t alternates[2];
+    const uint8_t *pattern;
+    const uint8_t *patch;
+    int patches = 0;
+    off_t pos;
+    uint8_t *rom;
+
+    rom = g_malloc(s->rom_size);
+    cpu_physical_memory_rw(rom_paddr, rom, s->rom_size, 0);
+
+    for (pos = 0; pos < s->rom_size - sizeof(vmcall_pattern); pos++) {
+        if (kvm_irqchip_in_kernel()) {
+            pattern = outl_pattern;
+            alternates[0] = outl_pattern[7];
+            alternates[1] = outl_pattern[7];
+            patch = &vmcall_pattern[5];
+        } else {
+            pattern = vmcall_pattern;
+            alternates[0] = vmcall_pattern[7];
+            alternates[1] = 0xd9; /* AMD's VMMCALL */
+            patch = &outl_pattern[5];
+        }
+        if (memcmp(rom + pos, pattern, 7) == 0 &&
+            (rom[pos + 7] == alternates[0] || rom[pos + 7] == alternates[1])) {
+            cpu_physical_memory_rw(rom_paddr + pos + 5, (uint8_t *)patch,
+                                   3, 1);
+            /*
+             * Don't flush the tb here. Under ordinary conditions, the patched
+             * calls are miles away from the current IP. Under malicious
+             * conditions, the guest could trick us to crash.
+             */
+        }
+    }
+
+    g_free(rom);
+
+    if (patches != 0 && patches != 2) {
+        return -1;
+    }
+
+    return 0;
+}
+
+/*
+ * For TCG mode or the time KVM honors read-only memory regions, we need to
+ * enable write access to the option ROM so that variables can be updated by
+ * the guest.
+ */
+static void vapic_map_rom_writable(VAPICROMState *s)
+{
+    target_phys_addr_t rom_paddr = s->rom_state_paddr & ROM_BLOCK_MASK;
+    MemoryRegionSection section;
+    MemoryRegion *as;
+    size_t rom_size;
+    uint8_t *ram;
+
+    as = sysbus_address_space(&s->busdev);
+
+    if (s->rom_mapped_writable) {
+        memory_region_del_subregion(as, &s->rom);
+        memory_region_destroy(&s->rom);
+    }
+
+    /* grab RAM memory region (region @rom_paddr may still be pc.rom) */
+    section = memory_region_find(as, 0, 1);
+
+    /* read ROM size from RAM region */
+    ram = memory_region_get_ram_ptr(section.mr);
+    rom_size = ram[rom_paddr + 2] * ROM_BLOCK_SIZE;
+    s->rom_size = rom_size;
+
+    /* We need to round up to avoid creating subpages
+     * from which we cannot run code. */
+    rom_size = TARGET_PAGE_ALIGN(rom_size);
+
+    memory_region_init_alias(&s->rom, "kvmvapic-rom", section.mr, rom_paddr,
+                             rom_size);
+    memory_region_add_subregion_overlap(as, rom_paddr, &s->rom, 1000);
+    s->rom_mapped_writable = true;
+}
+
+static int vapic_prepare(VAPICROMState *s)
+{
+    vapic_map_rom_writable(s);
+
+    if (patch_hypercalls(s) < 0) {
+        return -1;
+    }
+
+    vapic_enable_tpr_reporting(true);
+
+    return 0;
+}
+
+static void vapic_write(void *opaque, target_phys_addr_t addr, uint64_t data,
+                        unsigned int size)
+{
+    CPUState *env = cpu_single_env;
+    target_phys_addr_t rom_paddr;
+    VAPICROMState *s = opaque;
+
+    cpu_synchronize_state(env);
+
+    /*
+     * The VAPIC supports two PIO-based hypercalls, both via port 0x7E.
+     *  o 16-bit write access:
+     *    Reports the option ROM initialization to the hypervisor. Written
+     *    value is the offset of the state structure in the ROM.
+     *  o 8-bit write access:
+     *    Reactivates the VAPIC after a guest hibernation, i.e. after the
+     *    option ROM content has been re-initialized by a guest power cycle.
+     *  o 32-bit write access:
+     *    Poll for pending IRQs, considering the current VAPIC state.
+     */
+    switch (size) {
+    case 2:
+        if (s->state == VAPIC_INACTIVE) {
+            rom_paddr = (env->segs[R_CS].base + env->eip) & ROM_BLOCK_MASK;
+            s->rom_state_paddr = rom_paddr + data;
+
+            s->state = VAPIC_STANDBY;
+        }
+        if (vapic_prepare(s) < 0) {
+            s->state = VAPIC_INACTIVE;
+            break;
+        }
+        break;
+    case 1:
+        if (kvm_enabled()) {
+            /*
+             * Disable triggering instruction in ROM by writing a NOP.
+             *
+             * We cannot do this in TCG mode as the reported IP is not
+             * accurate.
+             */
+            pause_all_vcpus();
+            patch_byte(env, env->eip - 2, 0x66);
+            patch_byte(env, env->eip - 1, 0x90);
+            resume_all_vcpus();
+        }
+
+        if (s->state == VAPIC_ACTIVE) {
+            break;
+        }
+        if (update_rom_mapping(s, env, env->eip) < 0) {
+            break;
+        }
+        if (find_real_tpr_addr(s, env) < 0) {
+            break;
+        }
+        vapic_enable(s, env);
+        break;
+    default:
+    case 4:
+        if (!kvm_irqchip_in_kernel()) {
+            apic_poll_irq(env->apic_state);
+        }
+        break;
+    }
+}
+
+static const MemoryRegionOps vapic_ops = {
+    .write = vapic_write,
+    .endianness = DEVICE_NATIVE_ENDIAN,
+};
+
+static int vapic_init(SysBusDevice *dev)
+{
+    VAPICROMState *s = FROM_SYSBUS(VAPICROMState, dev);
+
+    memory_region_init_io(&s->io, &vapic_ops, s, "kvmvapic", 2);
+    sysbus_add_io(dev, VAPIC_IO_PORT, &s->io);
+    sysbus_init_ioports(dev, VAPIC_IO_PORT, 2);
+
+    option_rom[nb_option_roms].name = "kvmvapic.bin";
+    option_rom[nb_option_roms].bootindex = -1;
+    nb_option_roms++;
+
+    return 0;
+}
+
+static void do_vapic_enable(void *data)
+{
+    VAPICROMState *s = data;
+
+    vapic_enable(s, first_cpu);
+}
+
+static int vapic_post_load(void *opaque, int version_id)
+{
+    VAPICROMState *s = opaque;
+    uint8_t *zero;
+
+    /*
+     * The old implementation of qemu-kvm did not provide the state
+     * VAPIC_STANDBY. Reconstruct it.
+     */
+    if (s->state == VAPIC_INACTIVE && s->rom_state_paddr != 0) {
+        s->state = VAPIC_STANDBY;
+    }
+
+    if (s->state != VAPIC_INACTIVE) {
+        if (vapic_prepare(s) < 0) {
+            return -1;
+        }
+    }
+    if (s->state == VAPIC_ACTIVE) {
+        if (smp_cpus == 1) {
+            run_on_cpu(first_cpu, do_vapic_enable, s);
+        } else {
+            zero = g_malloc0(s->rom_state.vapic_size);
+            cpu_physical_memory_rw(s->vapic_paddr, zero,
+                                   s->rom_state.vapic_size, 1);
+            g_free(zero);
+        }
+    }
+
+    return 0;
+}
+
+static const VMStateDescription vmstate_handlers = {
+    .name = "kvmvapic-handlers",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .minimum_version_id_old = 1,
+    .fields = (VMStateField[]) {
+        VMSTATE_UINT32(set_tpr, VAPICHandlers),
+        VMSTATE_UINT32(set_tpr_eax, VAPICHandlers),
+        VMSTATE_UINT32_ARRAY(get_tpr, VAPICHandlers, 8),
+        VMSTATE_UINT32(get_tpr_stack, VAPICHandlers),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+static const VMStateDescription vmstate_guest_rom = {
+    .name = "kvmvapic-guest-rom",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .minimum_version_id_old = 1,
+    .fields = (VMStateField[]) {
+        VMSTATE_UNUSED(8),     /* signature */
+        VMSTATE_UINT32(vaddr, GuestROMState),
+        VMSTATE_UINT32(fixup_start, GuestROMState),
+        VMSTATE_UINT32(fixup_end, GuestROMState),
+        VMSTATE_UINT32(vapic_vaddr, GuestROMState),
+        VMSTATE_UINT32(vapic_size, GuestROMState),
+        VMSTATE_UINT32(vcpu_shift, GuestROMState),
+        VMSTATE_UINT32(real_tpr_addr, GuestROMState),
+        VMSTATE_STRUCT(up, GuestROMState, 0, vmstate_handlers, VAPICHandlers),
+        VMSTATE_STRUCT(mp, GuestROMState, 0, vmstate_handlers, VAPICHandlers),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+static const VMStateDescription vmstate_vapic = {
+    .name = "kvm-tpr-opt",      /* compatible with qemu-kvm VAPIC */
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .minimum_version_id_old = 1,
+    .post_load = vapic_post_load,
+    .fields = (VMStateField[]) {
+        VMSTATE_STRUCT(rom_state, VAPICROMState, 0, vmstate_guest_rom,
+                       GuestROMState),
+        VMSTATE_UINT32(state, VAPICROMState),
+        VMSTATE_UINT32(real_tpr_addr, VAPICROMState),
+        VMSTATE_UINT32(rom_state_vaddr, VAPICROMState),
+        VMSTATE_UINT32(vapic_paddr, VAPICROMState),
+        VMSTATE_UINT32(rom_state_paddr, VAPICROMState),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
+static void vapic_class_init(ObjectClass *klass, void *data)
+{
+    SysBusDeviceClass *sc = SYS_BUS_DEVICE_CLASS(klass);
+    DeviceClass *dc = DEVICE_CLASS(klass);
+
+    dc->no_user = 1;
+    dc->reset   = vapic_reset;
+    dc->vmsd    = &vmstate_vapic;
+    sc->init    = vapic_init;
+}
+
+static TypeInfo vapic_type = {
+    .name          = "kvmvapic",
+    .parent        = TYPE_SYS_BUS_DEVICE,
+    .instance_size = sizeof(VAPICROMState),
+    .class_init    = vapic_class_init,
+};
+
+static void vapic_register(void)
+{
+    type_register_static(&vapic_type);
+}
+
+type_init(vapic_register);