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[Xen-devel] [PATCH 2/3] kvm hypervisor : Add hypercalls to support pv-ti

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: [Xen-devel] [PATCH 2/3] kvm hypervisor : Add hypercalls to support pv-ticketlock
From: Srivatsa Vaddagiri <vatsa@xxxxxxxxxxxxxxxxxx>
Date: Wed, 19 Jan 2011 22:42:39 +0530
Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>, Nick Piggin <npiggin@xxxxxxxxx>, kvm@xxxxxxxxxxxxxxx, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, Eric Dumazet <dada1@xxxxxxxxxxxxx>, Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, suzuki@xxxxxxxxxx, Avi Kivity <avi@xxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Américo Wang <xiyou.wangcong@xxxxxxxxx>, Linux Virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>
Delivery-date: Wed, 19 Jan 2011 09:13:40 -0800
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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.


Signed-off-by: Srivatsa Vaddagiri <vatsa@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Suzuki Poulose <suzuki@xxxxxxxxxx>

---
 arch/x86/include/asm/kvm_para.h |    2 +
 arch/x86/kvm/x86.c              |   69 +++++++++++++++++++++++++++++++++++++++-
 include/linux/kvm.h             |    1 
 include/linux/kvm_host.h        |    1 
 include/linux/kvm_para.h        |    2 +
 virt/kvm/kvm_main.c             |    1 
 6 files changed, 75 insertions(+), 1 deletion(-)

Index: linux-2.6.37/arch/x86/include/asm/kvm_para.h
===================================================================
--- linux-2.6.37.orig/arch/x86/include/asm/kvm_para.h
+++ linux-2.6.37/arch/x86/include/asm/kvm_para.h
@@ -16,6 +16,8 @@
 #define KVM_FEATURE_CLOCKSOURCE                0
 #define KVM_FEATURE_NOP_IO_DELAY       1
 #define KVM_FEATURE_MMU_OP             2
+#define KVM_FEATURE_WAIT_FOR_KICK       4
+
 /* This indicates that the new set of kvmclock msrs
  * are available. The use of 0x11 and 0x12 is deprecated
  */
Index: linux-2.6.37/arch/x86/kvm/x86.c
===================================================================
--- linux-2.6.37.orig/arch/x86/kvm/x86.c
+++ linux-2.6.37/arch/x86/kvm/x86.c
@@ -1922,6 +1922,7 @@ int kvm_dev_ioctl_check_extension(long e
        case KVM_CAP_DEBUGREGS:
        case KVM_CAP_X86_ROBUST_SINGLESTEP:
        case KVM_CAP_XSAVE:
+       case KVM_CAP_WAIT_FOR_KICK:
                r = 1;
                break;
        case KVM_CAP_COALESCED_MMIO:
@@ -2340,7 +2341,8 @@ static void do_cpuid_ent(struct kvm_cpui
                entry->eax = (1 << KVM_FEATURE_CLOCKSOURCE) |
                             (1 << KVM_FEATURE_NOP_IO_DELAY) |
                             (1 << KVM_FEATURE_CLOCKSOURCE2) |
-                            (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT);
+                            (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT) |
+                            (1 << KVM_FEATURE_WAIT_FOR_KICK);
                entry->ebx = 0;
                entry->ecx = 0;
                entry->edx = 0;
@@ -4766,6 +4768,63 @@ int kvm_hv_hypercall(struct kvm_vcpu *vc
        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);
+
+       do {
+               /*
+                * Somebody has already tried kicking us. Acknowledge that
+                * and terminate the wait.
+                */
+               if (vcpu->kicked) {
+                       vcpu->kicked = 0;
+                       break;
+               }
+
+               /* 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);
+
+       } while (0);
+
+       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;
@@ -4802,6 +4861,14 @@ int kvm_emulate_hypercall(struct kvm_vcp
        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;
Index: linux-2.6.37/include/linux/kvm.h
===================================================================
--- linux-2.6.37.orig/include/linux/kvm.h
+++ linux-2.6.37/include/linux/kvm.h
@@ -540,6 +540,7 @@ struct kvm_ppc_pvinfo {
 #endif
 #define KVM_CAP_PPC_GET_PVINFO 57
 #define KVM_CAP_PPC_IRQ_LEVEL 58
+#define KVM_CAP_WAIT_FOR_KICK 59
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
Index: linux-2.6.37/include/linux/kvm_host.h
===================================================================
--- linux-2.6.37.orig/include/linux/kvm_host.h
+++ linux-2.6.37/include/linux/kvm_host.h
@@ -105,6 +105,7 @@ struct kvm_vcpu {
 #endif
 
        struct kvm_vcpu_arch arch;
+       int kicked;
 };
 
 /*
Index: linux-2.6.37/include/linux/kvm_para.h
===================================================================
--- linux-2.6.37.orig/include/linux/kvm_para.h
+++ linux-2.6.37/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
Index: linux-2.6.37/virt/kvm/kvm_main.c
===================================================================
--- linux-2.6.37.orig/virt/kvm/kvm_main.c
+++ linux-2.6.37/virt/kvm/kvm_main.c
@@ -185,6 +185,7 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu,
        vcpu->cpu = -1;
        vcpu->kvm = kvm;
        vcpu->vcpu_id = id;
+       vcpu->kicked = 0;
        init_waitqueue_head(&vcpu->wq);
 
        page = alloc_page(GFP_KERNEL | __GFP_ZERO);

 

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