Inform C2 state support via ACPI's CST per-processor package's, but
write an invalid latency value the first time the guest attempts to idle
via P_LVL2 port.

This way the TSC is considered unreliable, and we get away with the
costs relative to APIC timer broadcasts on enter/exit necessary for C1+.

It would be nice to fallback to plain hlt idle instead of C1, which
does not use the pmtimer for idle measurement, but Linux guests with
CONFIG_CPUIDLE enabled fallback to poll_idle instead which is very
inefficient.


Index: kvm-userspace.realtip/bios/acpi-dsdt.dsl
===================================================================
--- kvm-userspace.realtip.orig/bios/acpi-dsdt.dsl
+++ kvm-userspace.realtip/bios/acpi-dsdt.dsl
@@ -33,8 +33,20 @@ DefinitionBlock (
                PRU, 8,
                PRD, 8,
        }
+        OperationRegion(PWNO, SystemIO, 0xb040, 0x02)
+        Field (PWNO, WordAcc, NoLock, WriteAsZeros)
+        {
+                PWC, 16,
+        }
 
-        Processor (CPU0, 0x00, 0x0000b010, 0x06) {Method (_STA) { Return(0xF)}}
+        Processor (CPU0, 0x00, 0x0000b010, 0x06) {
+            Method (_STA) { Return(0xF)}
+                Name(_CST, Package() {
+                    1, Package() {
+                        ResourceTemplate() {Register(SystemIO, 8, 0, 0xb014)},
+                        2, 2, 300},
+                    })
+        }
         Processor (CPU1, 0x01, 0x0000b010, 0x06) {
             Name (TMP, Buffer(0x8) {0x0, 0x8, 0x01, 0x01, 0x1, 0x0, 0x0, 0x0})
             Method(_MAT, 0) {
@@ -44,6 +56,11 @@ DefinitionBlock (
             Method (_STA) {
                 Return(0xF)
             }
+            Name(_CST, Package() {
+                1, Package() {
+                    ResourceTemplate() {Register(SystemIO, 8, 0, 0xb014)},
+                    2, 2, 300},
+            })
         }
         Processor (CPU2, 0x02, 0x0000b010, 0x06) {
             Name (TMP, Buffer(0x8) {0x0, 0x8, 0x02, 0x02, 0x1, 0x0, 0x0, 0x0})
@@ -54,6 +71,11 @@ DefinitionBlock (
             Method (_STA) {
                 Return(0xF)
             }
+            Name(_CST, Package() {
+                1, Package() {
+                    ResourceTemplate() {Register(SystemIO, 8, 0, 0xb014)},
+                    2, 2, 300},
+            })
         }
         Processor (CPU3, 0x03, 0x0000b010, 0x06) {
             Name (TMP, Buffer(0x8) {0x0, 0x8, 0x03, 0x03, 0x1, 0x0, 0x0, 0x0})
@@ -64,6 +86,11 @@ DefinitionBlock (
             Method (_STA) {
                 Return(0xF)
             }
+            Name(_CST, Package() {
+                1, Package() {
+                    ResourceTemplate() {Register(SystemIO, 8, 0, 0xb014)},
+                    2, 2, 300},
+            })
         }
         Processor (CPU4, 0x04, 0x0000b010, 0x06) {
             Name (TMP, Buffer(0x8) {0x0, 0x8, 0x04, 0x04, 0x1, 0x0, 0x0, 0x0})
@@ -74,6 +101,11 @@ DefinitionBlock (
             Method (_STA) {
                 Return(0xF)
             }
+            Name(_CST, Package() {
+                1, Package() {
+                    ResourceTemplate() {Register(SystemIO, 8, 0, 0xb014)},
+                    2, 2, 300},
+            })
         }
         Processor (CPU5, 0x05, 0x0000b010, 0x06) {
             Name (TMP, Buffer(0x8) {0x0, 0x8, 0x05, 0x05, 0x1, 0x0, 0x0, 0x0})
@@ -84,6 +116,11 @@ DefinitionBlock (
             Method (_STA) {
                 Return(0xF)
             }
+            Name(_CST, Package() {
+                1, Package() {
+                    ResourceTemplate() {Register(SystemIO, 8, 0, 0xb014)},
+                    2, 2, 300},
+            })
         }
         Processor (CPU6, 0x06, 0x0000b010, 0x06) {
             Name (TMP, Buffer(0x8) {0x0, 0x8, 0x06, 0x06, 0x1, 0x0, 0x0, 0x0})
@@ -94,6 +131,11 @@ DefinitionBlock (
             Method (_STA) {
                 Return(0xF)
             }
+            Name(_CST, Package() {
+                1, Package() {
+                    ResourceTemplate() {Register(SystemIO, 8, 0, 0xb014)},
+                    2, 2, 300},
+            })
         }
         Processor (CPU7, 0x07, 0x0000b010, 0x06) {
             Name (TMP, Buffer(0x8) {0x0, 0x8, 0x07, 0x07, 0x1, 0x0, 0x0, 0x0})
@@ -104,6 +146,11 @@ DefinitionBlock (
             Method (_STA) {
                 Return(0xF)
             }
+            Name(_CST, Package() {
+                1, Package() {
+                    ResourceTemplate() {Register(SystemIO, 8, 0, 0xb014)},
+                    2, 2, 300},
+            })
         }
         Processor (CPU8, 0x08, 0x0000b010, 0x06) {
             Name (TMP, Buffer(0x8) {0x0, 0x8, 0x08, 0x08, 0x1, 0x0, 0x0, 0x0})
@@ -114,6 +161,11 @@ DefinitionBlock (
             Method (_STA) {
                 Return(0xF)
             }
+            Name(_CST, Package() {
+                1, Package() {
+                    ResourceTemplate() {Register(SystemIO, 8, 0, 0xb014)},
+                    2, 2, 300},
+            })
         }
         Processor (CPU9, 0x09, 0x0000b010, 0x06) {
             Name (TMP, Buffer(0x8) {0x0, 0x8, 0x09, 0x09, 0x1, 0x0, 0x0, 0x0})
@@ -124,6 +176,11 @@ DefinitionBlock (
             Method (_STA) {
                 Return(0xF)
             }
+            Name(_CST, Package() {
+                1, Package() {
+                    ResourceTemplate() {Register(SystemIO, 8, 0, 0xb014)},
+                    2, 2, 300},
+            })
         }
         Processor (CPUA, 0x0a, 0x0000b010, 0x06) {
             Name (TMP, Buffer(0x8) {0x0, 0x8, 0x0A, 0x0A, 0x1, 0x0, 0x0, 0x0})
@@ -134,6 +191,11 @@ DefinitionBlock (
             Method (_STA) {
                 Return(0xF)
             }
+            Name(_CST, Package() {
+                1, Package() {
+                    ResourceTemplate() {Register(SystemIO, 8, 0, 0xb014)},
+                    2, 2, 300},
+            })
         }
         Processor (CPUB, 0x0b, 0x0000b010, 0x06) {
             Name (TMP, Buffer(0x8) {0x0, 0x8, 0x0B, 0x0B, 0x1, 0x0, 0x0, 0x0})
@@ -144,6 +206,11 @@ DefinitionBlock (
             Method (_STA) {
                 Return(0xF)
             }
+            Name(_CST, Package() {
+                1, Package() {
+                    ResourceTemplate() {Register(SystemIO, 8, 0, 0xb014)},
+                    2, 2, 300},
+            })
         }
         Processor (CPUC, 0x0c, 0x0000b010, 0x06) {
             Name (TMP, Buffer(0x8) {0x0, 0x8, 0x0C, 0x0C, 0x1, 0x0, 0x0, 0x0})
@@ -154,6 +221,11 @@ DefinitionBlock (
             Method (_STA) {
                 Return(0xF)
             }
+            Name(_CST, Package() {
+                1, Package() {
+                    ResourceTemplate() {Register(SystemIO, 8, 0, 0xb014)},
+                    2, 2, 300},
+            })
         }
         Processor (CPUD, 0x0d, 0x0000b010, 0x06) {
             Name (TMP, Buffer(0x8) {0x0, 0x8, 0x0D, 0x0D, 0x1, 0x0, 0x0, 0x0})
@@ -164,6 +236,11 @@ DefinitionBlock (
             Method (_STA) {
                 Return(0xF)
             }
+            Name(_CST, Package() {
+                1, Package() {
+                    ResourceTemplate() {Register(SystemIO, 8, 0, 0xb014)},
+                    2, 2, 300},
+            })
         }
         Processor (CPUE, 0x0e, 0x0000b010, 0x06) {
             Name (TMP, Buffer(0x8) {0x0, 0x8, 0x0E, 0x0E, 0x1, 0x0, 0x0, 0x0})
@@ -174,6 +251,11 @@ DefinitionBlock (
             Method (_STA) {
                 Return(0xF)
             }
+            Name(_CST, Package() {
+                1, Package() {
+                    ResourceTemplate() {Register(SystemIO, 8, 0, 0xb014)},
+                    2, 2, 300},
+            })
         }
     }
 
@@ -1544,6 +1626,81 @@ DefinitionBlock (
             Return(0x01)
         }
         Method(_L06) {
+            If (And(\_PR.PWC, 0x1)) {
+                Store (0xfffff, Index (DeRefOf (Index (\_PR.CPU0._CST, 1)), 2))
+                Notify(\_PR.CPU0, 0x81)
+            }
+
+            If (And(\_PR.PWC, 0x2)) {
+                Store (0xfffff, Index (DeRefOf (Index (\_PR.CPU1._CST, 1)), 2))
+                Notify(\_PR.CPU1, 0x81)
+            }
+
+            If (And(\_PR.PWC, 0x4)) {
+                Store (0xfffff, Index (DeRefOf (Index (\_PR.CPU2._CST, 1)), 2))
+                Notify(\_PR.CPU2, 0x81)
+            }
+
+            If (And(\_PR.PWC, 0x8)) {
+                Store (0xfffff, Index (DeRefOf (Index (\_PR.CPU3._CST, 1)), 2))
+                Notify(\_PR.CPU3, 0x81)
+            }
+
+            If (And(\_PR.PWC, 0x10)) {
+                Store (0xfffff, Index (DeRefOf (Index (\_PR.CPU4._CST, 1)), 2))
+                Notify(\_PR.CPU4, 0x81)
+            }
+
+            If (And(\_PR.PWC, 0x20)) {
+                Store (0xfffff, Index (DeRefOf (Index (\_PR.CPU5._CST, 1)), 2))
+                Notify(\_PR.CPU5, 0x81)
+            }
+
+            If (And(\_PR.PWC, 0x40)) {
+                Store (0xfffff, Index (DeRefOf (Index (\_PR.CPU6._CST, 1)), 2))
+                Notify(\_PR.CPU6, 0x81)
+            }
+
+            If (And(\_PR.PWC, 0x80)) {
+                Store (0xfffff, Index (DeRefOf (Index (\_PR.CPU7._CST, 1)), 2))
+                Notify(\_PR.CPU7, 0x81)
+            }
+
+            If (And(\_PR.PWC, 0x100)) {
+                Store (0xfffff, Index (DeRefOf (Index (\_PR.CPU8._CST, 1)), 2))
+                Notify(\_PR.CPU8, 0x81)
+            }
+
+            If (And(\_PR.PWC, 0x200)) {
+                Store (0xfffff, Index (DeRefOf (Index (\_PR.CPU9._CST, 1)), 2))
+                Notify(\_PR.CPU9, 0x81)
+            }
+
+            If (And(\_PR.PWC, 0x400)) {
+                Store (0xfffff, Index (DeRefOf (Index (\_PR.CPUA._CST, 1)), 2))
+                Notify(\_PR.CPUA, 0x81)
+            }
+
+            If (And(\_PR.PWC, 0x800)) {
+                Store (0xfffff, Index (DeRefOf (Index (\_PR.CPUB._CST, 1)), 2))
+                Notify(\_PR.CPUB, 0x81)
+            }
+
+            If (And(\_PR.PWC, 0x1000)) {
+                Store (0xfffff, Index (DeRefOf (Index (\_PR.CPUC._CST, 1)), 2))
+                Notify(\_PR.CPUC, 0x81)
+            }
+
+            If (And(\_PR.PWC, 0x2000)) {
+                Store (0xfffff, Index (DeRefOf (Index (\_PR.CPUD._CST, 1)), 2))
+                Notify(\_PR.CPUD, 0x81)
+            }
+
+            If (And(\_PR.PWC, 0x4000)) {
+                Store (0xfffff, Index (DeRefOf (Index (\_PR.CPUE._CST, 1)), 2))
+                Notify(\_PR.CPUE, 0x81)
+            }
+
             Return(0x01)
         }
         Method(_L07) {
Index: kvm-userspace.realtip/qemu/hw/acpi.c
===================================================================
--- kvm-userspace.realtip.orig/qemu/hw/acpi.c
+++ kvm-userspace.realtip/qemu/hw/acpi.c
@@ -121,6 +121,31 @@ static void pm_tmr_timer(void *opaque)
     pm_update_sci(s);
 }
 
+/*
+ * Fake C2 emulation, so the OS will consider the TSC unreliable
+ * an fallback to C1 after the latency is updated to a high value
+ * in acpi-dsdt.dsl.
+ */
+static void qemu_system_cpu_power_notify(int cpu);
+static uint32_t pm_ioport_readb(void *opaque, uint32_t addr)
+{
+    CPUState *env = cpu_single_env;
+
+    addr &= 0x3f;
+    switch (addr) {
+    case 0x14: /* P_LVL2 */
+         qemu_system_cpu_power_notify(env->cpu_index);
+    }
+#ifdef DEBUG
+    printf("pm_ioport_readb addr=%x\n", addr);
+#endif
+    return 0;
+}
+
+static void pm_ioport_writeb(void *opaque, uint32_t addr, uint32_t val)
+{
+}
+
 static void pm_ioport_writew(void *opaque, uint32_t addr, uint32_t val)
 {
     PIIX4PMState *s = opaque;
@@ -420,6 +445,8 @@ static void pm_io_space_update(PIIX4PMSt
 #if defined(DEBUG)
         printf("PM: mapping to 0x%x\n", pm_io_base);
 #endif
+        register_ioport_write(pm_io_base, 64, 1, pm_ioport_writeb, s);
+        register_ioport_read(pm_io_base, 64, 1, pm_ioport_readb, s);
         register_ioport_write(pm_io_base, 64, 2, pm_ioport_writew, s);
         register_ioport_read(pm_io_base, 64, 2, pm_ioport_readw, s);
         register_ioport_write(pm_io_base, 64, 4, pm_ioport_writel, s);
@@ -538,6 +565,7 @@ void qemu_system_powerdown(void)
 }
 #endif
 #define GPE_BASE 0xafe0
+#define POWER_GPE_BASE 0xb040
 #define PROC_BASE 0xaf00
 #define PCI_BASE 0xae00
 #define PCI_EJ_BASE 0xae08
@@ -554,7 +582,12 @@ struct pci_status {
     uint32_t down;
 };
 
+struct power_gpe_regs {
+    uint8_t cpus;
+};
+
 static struct gpe_regs gpe;
+static struct power_gpe_regs power_gpe;
 static struct pci_status pci0_status;
 
 static uint32_t gpe_readb(void *opaque, uint32_t addr)
@@ -623,6 +656,23 @@ static void gpe_writeb(void *opaque, uin
 #endif
 }
 
+static uint32_t cpu_power_read(void *opaque, uint32_t addr)
+{
+    struct power_gpe_regs *p = opaque;
+
+#if defined(DEBUG)
+    printf("cpu power read %lx == %lx\n", addr, p->cpus);
+#endif
+    return p->cpus;
+}
+
+static void cpu_power_write(void *opaque, uint32_t addr, uint32_t val)
+{
+#if defined(DEBUG)
+    printf("cpu power write %lx <== %lx\n", addr, val);
+#endif
+}
+
 static uint32_t pcihotplug_read(void *opaque, uint32_t addr)
 {
     uint32_t val = 0;
@@ -696,6 +746,9 @@ void qemu_system_hot_add_init(const char
     register_ioport_write(PCI_EJ_BASE, 4, 4, pciej_write, NULL);
     register_ioport_read(PCI_EJ_BASE, 4, 4,  pciej_read, NULL);
 
+    register_ioport_write(POWER_GPE_BASE, 4, 2, cpu_power_write, &power_gpe);
+    register_ioport_read(POWER_GPE_BASE, 4, 2, cpu_power_read, &power_gpe);
+
     model = cpu_model;
 }
 
@@ -738,6 +791,16 @@ void qemu_system_cpu_hot_add(int cpu, in
         disable_processor(&gpe, cpu);
     qemu_set_irq(pm_state->irq, 0);
 }
+
+static void qemu_system_cpu_power_notify(int cpu)
+{
+    power_gpe.cpus = 0;
+
+    qemu_set_irq(pm_state->irq, 1);
+    power_gpe.cpus |= (1 << cpu);
+    qemu_set_irq(pm_state->irq, 0);
+}
+
 #endif
 
 static void enable_device(struct pci_status *p, struct gpe_regs *g, int slot)

-- 

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