[PATCH 2/3] kvm hypervisor : Add hypercalls to supportpv-ticketlock

From: Srivatsa Vaddagiri
Date: Wed Jan 19 2011 - 12:12:50 EST

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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