2 files changed, 61 insertions, 3 deletions

diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
index 63ab1661d00e..2f7712e08b1e 100644
--- a/arch/x86/include/asm/kvm_para.h
+++ b/arch/x86/include/asm/kvm_para.h
@@ -22,6 +22,7 @@
 #define KVM_FEATURE_CLOCKSOURCE2        3
 #define KVM_FEATURE_ASYNC_PF            4
 #define KVM_FEATURE_STEAL_TIME          5
+#define KVM_FEATURE_PV_EOI              6
 
 /* The last 8 bits are used to indicate how to interpret the flags field
  * in pvclock structure. If no bits are set, all flags are ignored.
@@ -37,6 +38,7 @@
 #define MSR_KVM_SYSTEM_TIME_NEW 0x4b564d01
 #define MSR_KVM_ASYNC_PF_EN 0x4b564d02
 #define MSR_KVM_STEAL_TIME  0x4b564d03
+#define MSR_KVM_PV_EOI_EN      0x4b564d04
 
 struct kvm_steal_time {
         __u64 steal;
@@ -89,6 +91,11 @@ struct kvm_vcpu_pv_apf_data {
         __u32 enabled;
 };
 
+#define KVM_PV_EOI_BIT 0
+#define KVM_PV_EOI_MASK (0x1 << KVM_PV_EOI_BIT)
+#define KVM_PV_EOI_ENABLED KVM_PV_EOI_MASK
+#define KVM_PV_EOI_DISABLED 0x0
+
 #ifdef __KERNEL__
 #include <asm/processor.h>
 
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index e554e5ad2fe8..75ab94c75c7a 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -39,6 +39,8 @@
 #include <asm/desc.h>
 #include <asm/tlbflush.h>
 #include <asm/idle.h>
+#include <asm/apic.h>
+#include <asm/apicdef.h>
 
 static int kvmapf = 1;
 
@@ -283,6 +285,22 @@ static void kvm_register_steal_time(void)
                 cpu, __pa(st));
 }
 
+static DEFINE_PER_CPU(unsigned long, kvm_apic_eoi) = KVM_PV_EOI_DISABLED;
+
+static void kvm_guest_apic_eoi_write(u32 reg, u32 val)
+{
+        /**
+         * This relies on __test_and_clear_bit to modify the memory
+         * in a way that is atomic with respect to the local CPU.
+         * The hypervisor only accesses this memory from the local CPU so
+         * there's no need for lock or memory barriers.
+         * An optimization barrier is implied in apic write.
+         */
+        if (__test_and_clear_bit(KVM_PV_EOI_BIT, &__get_cpu_var(kvm_apic_eoi)))
+                return;
+        apic->write(APIC_EOI, APIC_EOI_ACK);
+}
+
 void __cpuinit kvm_guest_cpu_init(void)
 {
         if (!kvm_para_available())
@@ -300,11 +318,20 @@ void __cpuinit kvm_guest_cpu_init(void)
                        smp_processor_id());
         }
 
+        if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) {
+                unsigned long pa;
+                /* Size alignment is implied but just to make it explicit. */
+                BUILD_BUG_ON(__alignof__(kvm_apic_eoi) < 4);
+                __get_cpu_var(kvm_apic_eoi) = 0;
+                pa = __pa(&__get_cpu_var(kvm_apic_eoi)) | KVM_MSR_ENABLED;
+                wrmsrl(MSR_KVM_PV_EOI_EN, pa);
+        }
+
         if (has_steal_clock)
                 kvm_register_steal_time();
 }
 
-static void kvm_pv_disable_apf(void *unused)
+static void kvm_pv_disable_apf(void)
 {
         if (!__get_cpu_var(apf_reason).enabled)
                 return;
@@ -316,11 +343,23 @@ static void kvm_pv_disable_apf(void *unused)
                smp_processor_id());
 }
 
+static void kvm_pv_guest_cpu_reboot(void *unused)
+{
+        /*
+         * We disable PV EOI before we load a new kernel by kexec,
+         * since MSR_KVM_PV_EOI_EN stores a pointer into old kernel's memory.
+         * New kernel can re-enable when it boots.
+         */
+        if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
+                wrmsrl(MSR_KVM_PV_EOI_EN, 0);
+        kvm_pv_disable_apf();
+}
+
 static int kvm_pv_reboot_notify(struct notifier_block *nb,
                                 unsigned long code, void *unused)
 {
         if (code == SYS_RESTART)
-                on_each_cpu(kvm_pv_disable_apf, NULL, 1);
+                on_each_cpu(kvm_pv_guest_cpu_reboot, NULL, 1);
         return NOTIFY_DONE;
 }
 
@@ -371,7 +410,9 @@ static void __cpuinit kvm_guest_cpu_online(void *dummy)
 static void kvm_guest_cpu_offline(void *dummy)
 {
         kvm_disable_steal_time();
-        kvm_pv_disable_apf(NULL);
+        if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
+                wrmsrl(MSR_KVM_PV_EOI_EN, 0);
+        kvm_pv_disable_apf();
         apf_task_wake_all();
 }
 
@@ -424,6 +465,16 @@ void __init kvm_guest_init(void)
                 pv_time_ops.steal_clock = kvm_steal_clock;
         }
 
+        if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) {
+                struct apic **drv;
+
+                for (drv = __apicdrivers; drv < __apicdrivers_end; drv++) {
+                        /* Should happen once for each apic */
+                        WARN_ON((*drv)->eoi_write == kvm_guest_apic_eoi_write);
+                        (*drv)->eoi_write = kvm_guest_apic_eoi_write;
+                }
+        }
+
 #ifdef CONFIG_SMP
         smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;
         register_cpu_notifier(&kvm_cpu_notifier);