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[Xen-devel] [PATCH RFC V2 3/5] kvm hypervisor : Add two hypercalls to su

To: Greg Kroah-Hartman <gregkh@xxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Gleb Natapov <gleb@xxxxxxxxxx>, Virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>, Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, x86@xxxxxxxxxx, KVM <kvm@xxxxxxxxxxxxxxx>, Dave Jiang <dave.jiang@xxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>, Xen <xen-devel@xxxxxxxxxxxxxxxxxxx>, Sedat Dilek <sedat.dilek@xxxxxxxxx>, Yinghai Lu <yinghai@xxxxxxxxxx>, Marcelo Tosatti <mtosatti@xxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Avi Kivity <avi@xxxxxxxxxx>, Rik van Riel <riel@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, LKML <linux-kernel@xxxxxxxxxxxxxxx>
Subject: [Xen-devel] [PATCH RFC V2 3/5] kvm hypervisor : Add two hypercalls to support pv-ticketlock
From: Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>
Date: Mon, 24 Oct 2011 00:35:59 +0530
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Suzuki Poulose <suzuki@xxxxxxxxxxxxxxxxxx>, Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>, Srivatsa Vaddagiri <vatsa@xxxxxxxxxxxxxxxxxx>
Delivery-date: Tue, 25 Oct 2011 09:42:17 -0700
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Add two hypercalls to KVM hypervisor to support pv-ticketlocks.
    
KVM_HC_WAIT_FOR_KICK blocks the calling vcpu until another vcpu kicks it or it
is woken up because of an event like interrupt.
   
KVM_HC_KICK_CPU allows the calling vcpu to kick another vcpu.
    
The presence of these hypercalls is indicated to guest via
KVM_FEATURE_WAIT_FOR_KICK/KVM_CAP_WAIT_FOR_KICK.

Qemu needs a corresponding patch to pass up the presence of this feature to 
guest via cpuid. Patch to qemu will be sent separately.

There is no Xen/KVM hypercall interface to await kick from.
    
Signed-off-by: Srivatsa Vaddagiri <vatsa@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Suzuki Poulose <suzuki@xxxxxxxxxx>
Signed-off-by: Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>
---
diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
index 734c376..2874c19 100644
--- a/arch/x86/include/asm/kvm_para.h
+++ b/arch/x86/include/asm/kvm_para.h
@@ -16,12 +16,14 @@
 #define KVM_FEATURE_CLOCKSOURCE                0
 #define KVM_FEATURE_NOP_IO_DELAY       1
 #define KVM_FEATURE_MMU_OP             2
+
 /* This indicates that the new set of kvmclock msrs
  * are available. The use of 0x11 and 0x12 is deprecated
  */
 #define KVM_FEATURE_CLOCKSOURCE2        3
 #define KVM_FEATURE_ASYNC_PF           4
 #define KVM_FEATURE_STEAL_TIME         5
+#define KVM_FEATURE_WAIT_FOR_KICK       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.
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 84a28ea..b43fd18 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2077,6 +2077,7 @@ int kvm_dev_ioctl_check_extension(long ext)
        case KVM_CAP_XSAVE:
        case KVM_CAP_ASYNC_PF:
        case KVM_CAP_GET_TSC_KHZ:
+       case KVM_CAP_WAIT_FOR_KICK:
                r = 1;
                break;
        case KVM_CAP_COALESCED_MMIO:
@@ -2548,7 +2549,8 @@ static void do_cpuid_ent(struct kvm_cpuid_entry2 *entry, 
u32 function,
                             (1 << KVM_FEATURE_NOP_IO_DELAY) |
                             (1 << KVM_FEATURE_CLOCKSOURCE2) |
                             (1 << KVM_FEATURE_ASYNC_PF) |
-                            (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT);
+                            (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT) |
+                            (1 << KVM_FEATURE_WAIT_FOR_KICK);
 
                if (sched_info_on())
                        entry->eax |= (1 << KVM_FEATURE_STEAL_TIME);
@@ -5231,6 +5233,61 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
        return 1;
 }
 
+/*
+ * kvm_pv_wait_for_kick_op : Block until kicked by either a KVM_HC_KICK_CPU
+ * hypercall or a event like interrupt.
+ *
+ * @vcpu : vcpu which is blocking.
+ */
+static void kvm_pv_wait_for_kick_op(struct kvm_vcpu *vcpu)
+{
+       DEFINE_WAIT(wait);
+
+       /*
+        * Blocking on vcpu->wq allows us to wake up sooner if required to
+        * service pending events (like interrupts).
+        *
+        * Also set state to TASK_INTERRUPTIBLE before checking vcpu->kicked to
+        * avoid racing with kvm_pv_kick_cpu_op().
+        */
+       prepare_to_wait(&vcpu->wq, &wait, TASK_INTERRUPTIBLE);
+
+       /*
+        * Somebody has already tried kicking us. Acknowledge that
+        * and terminate the wait.
+        */
+       if (vcpu->kicked) {
+               vcpu->kicked = 0;
+               goto end_wait;
+       }
+
+       /* Let's wait for either KVM_HC_KICK_CPU or someother event
+        * to wake us up.
+        */
+
+       srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+       schedule();
+       vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
+
+end_wait:
+       finish_wait(&vcpu->wq, &wait);
+}
+
+/*
+ * kvm_pv_kick_cpu_op:  Kick a vcpu.
+ *
+ * @cpu - vcpu to be kicked.
+ */
+static void kvm_pv_kick_cpu_op(struct kvm *kvm, int cpu)
+{
+       struct kvm_vcpu *vcpu = kvm_get_vcpu(kvm, cpu);
+
+       if (vcpu) {
+               vcpu->kicked = 1;
+               wake_up_interruptible(&vcpu->wq);
+       }
+}
+
 int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
 {
        unsigned long nr, a0, a1, a2, a3, ret;
@@ -5267,6 +5324,14 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
        case KVM_HC_MMU_OP:
                r = kvm_pv_mmu_op(vcpu, a0, hc_gpa(vcpu, a1, a2), &ret);
                break;
+       case KVM_HC_WAIT_FOR_KICK:
+               kvm_pv_wait_for_kick_op(vcpu);
+               ret = 0;
+               break;
+       case KVM_HC_KICK_CPU:
+               kvm_pv_kick_cpu_op(vcpu->kvm, a0);
+               ret = 0;
+               break;
        default:
                ret = -KVM_ENOSYS;
                break;
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index aace6b8..736acc0 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -553,6 +553,7 @@ struct kvm_ppc_pvinfo {
 #define KVM_CAP_SPAPR_TCE 63
 #define KVM_CAP_PPC_SMT 64
 #define KVM_CAP_PPC_RMA        65
+#define KVM_CAP_WAIT_FOR_KICK 66
 #define KVM_CAP_S390_GMAP 71
 
 #ifdef KVM_CAP_IRQ_ROUTING
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index eabb21a..2946563 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -152,6 +152,11 @@ struct kvm_vcpu {
 #endif
 
        struct kvm_vcpu_arch arch;
+
+       /*
+        * blocked vcpu wakes up by checking this flag set by unlocker
+        */
+       int kicked;
 };
 
 static inline int kvm_vcpu_exiting_guest_mode(struct kvm_vcpu *vcpu)
diff --git a/include/linux/kvm_para.h b/include/linux/kvm_para.h
index 47a070b..4efee4d 100644
--- a/include/linux/kvm_para.h
+++ b/include/linux/kvm_para.h
@@ -19,6 +19,8 @@
 #define KVM_HC_MMU_OP                  2
 #define KVM_HC_FEATURES                        3
 #define KVM_HC_PPC_MAP_MAGIC_PAGE      4
+#define KVM_HC_WAIT_FOR_KICK            5
+#define KVM_HC_KICK_CPU                        6
 
 /*
  * hypercalls use architecture specific
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index aefdda3..d09982d 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -224,6 +224,7 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, 
unsigned id)
        vcpu->kvm = kvm;
        vcpu->vcpu_id = id;
        vcpu->pid = NULL;
+       vcpu->kicked = 0;
        init_waitqueue_head(&vcpu->wq);
        kvm_async_pf_vcpu_init(vcpu);
 


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