Linux Virtualization - Aug 2013 - [PATCH V12 0/5] Paravirtualized ticket spinlocks for KVM host

This series forms the kvm host part of paravirtual spinlock
 based against kvm tree.
 
 Please refer https://lkml.org/lkml/2013/8/6/178 for kvm guest part
 of the series.

 Please note that:
 kvm uapi: Add KICK_CPU and PV_UNHALT definition to uapi is a common patch
 for both guest and host.

 Srivatsa Vaddagiri (1):
  kvm hypervisor : Add a hypercall to KVM hypervisor to support pv-ticketlocks

 Raghavendra K T (4):
  kvm uapi: Add KICK_CPU and PV_UNHALT definition to uapi
  kvm : Fold pv_unhalt flag into GET_MP_STATE ioctl to aid migration
  kvm hypervisor: Simplify kvm_for_each_vcpu with kvm_irq_delivery_to_apic
  Documentation/kvm : Add documentation on Hypercalls and features used for PV
spinlock
--- 
 Documentation/virtual/kvm/cpuid.txt      |  4 ++++
 Documentation/virtual/kvm/hypercalls.txt | 14 ++++++++++++++
 arch/x86/include/asm/kvm_host.h          |  5 +++++
 arch/x86/include/uapi/asm/kvm_para.h     |  1 +
 arch/x86/kvm/cpuid.c                     |  3 ++-
 arch/x86/kvm/lapic.c                     |  5 ++++-
 arch/x86/kvm/x86.c                       | 31 ++++++++++++++++++++++++++++++-
 include/uapi/linux/kvm_para.h            |  1 +
 8 files changed, 61 insertions(+), 3 deletions(-)

kvm uapi: Add KICK_CPU and PV_UNHALT definition to uapi

From: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>

this is needed by both guest and host.

Originally-from: Srivatsa Vaddagiri <vatsa at linux.vnet.ibm.com>
Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
Acked-by: Gleb Natapov <gleb at redhat.com>
Acked-by: Ingo Molnar <mingo at kernel.org>
---
 arch/x86/include/uapi/asm/kvm_para.h |    1 +
 include/uapi/linux/kvm_para.h        |    1 +
 2 files changed, 2 insertions(+)

diff --git a/arch/x86/include/uapi/asm/kvm_para.h
b/arch/x86/include/uapi/asm/kvm_para.h
index 06fdbd9..94dc8ca 100644
--- a/arch/x86/include/uapi/asm/kvm_para.h
+++ b/arch/x86/include/uapi/asm/kvm_para.h
@@ -23,6 +23,7 @@
 #define KVM_FEATURE_ASYNC_PF		4
 #define KVM_FEATURE_STEAL_TIME		5
 #define KVM_FEATURE_PV_EOI		6
+#define KVM_FEATURE_PV_UNHALT		7
 
 /* 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/include/uapi/linux/kvm_para.h b/include/uapi/linux/kvm_para.h
index cea2c5c..2841f86 100644
--- a/include/uapi/linux/kvm_para.h
+++ b/include/uapi/linux/kvm_para.h
@@ -19,6 +19,7 @@
 #define KVM_HC_MMU_OP			2
 #define KVM_HC_FEATURES			3
 #define KVM_HC_PPC_MAP_MAGIC_PAGE	4
+#define KVM_HC_KICK_CPU			5
 
 /*
  * hypercalls use architecture specific

kvm hypervisor : Add a hypercall to KVM hypervisor to support pv-ticketlocks

From: Srivatsa Vaddagiri <vatsa at linux.vnet.ibm.com>

kvm_hc_kick_cpu allows the calling vcpu to kick another vcpu out of halt state.
the presence of these hypercalls is indicated to guest via
kvm_feature_pv_unhalt.

Signed-off-by: Srivatsa Vaddagiri <vatsa at linux.vnet.ibm.com>
Signed-off-by: Suzuki Poulose <suzuki at in.ibm.com>
[Raghu: Apic related changes, folding pvunhalted into vcpu_runnable
 Added flags for future use (suggested by Gleb)]
Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
Acked-by: Gleb Natapov <gleb at redhat.com>
Acked-by: Ingo Molnar <mingo at kernel.org>
---
 arch/x86/include/asm/kvm_host.h |    5 +++++
 arch/x86/kvm/cpuid.c            |    3 ++-
 arch/x86/kvm/x86.c              |   37 +++++++++++++++++++++++++++++++++++++
 3 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index f87f7fc..1d1f711 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -511,6 +511,11 @@ struct kvm_vcpu_arch {
 	 * instruction.
 	 */
 	bool write_fault_to_shadow_pgtable;
+
+	/* pv related host specific info */
+	struct {
+		bool pv_unhalted;
+	} pv;
 };
 
 struct kvm_lpage_info {
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index a20ecb5..b110fe6 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -413,7 +413,8 @@ static int do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32
function,
 			     (1 << KVM_FEATURE_CLOCKSOURCE2) |
 			     (1 << KVM_FEATURE_ASYNC_PF) |
 			     (1 << KVM_FEATURE_PV_EOI) |
-			     (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT);
+			     (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT) |
+			     (1 << KVM_FEATURE_PV_UNHALT);
 
 		if (sched_info_on())
 			entry->eax |= (1 << KVM_FEATURE_STEAL_TIME);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d21bce5..dae4575 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5495,6 +5495,36 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
 	return 1;
 }
 
+/*
+ * kvm_pv_kick_cpu_op:  Kick a vcpu.
+ *
+ * @apicid - apicid of vcpu to be kicked.
+ */
+static void kvm_pv_kick_cpu_op(struct kvm *kvm, unsigned long flags, int
apicid)
+{
+	struct kvm_vcpu *vcpu = NULL;
+	int i;
+
+	kvm_for_each_vcpu(i, vcpu, kvm) {
+		if (!kvm_apic_present(vcpu))
+			continue;
+
+		if (kvm_apic_match_dest(vcpu, 0, 0, apicid, 0))
+			break;
+	}
+	if (vcpu) {
+		/*
+		 * Setting unhalt flag here can result in spurious runnable
+		 * state when unhalt reset does not happen in vcpu_block.
+		 * But that is harmless since that should soon result in halt.
+		 */
+		vcpu->arch.pv.pv_unhalted = true;
+		/* We need everybody see unhalt before vcpu unblocks */
+		smp_wmb();
+		kvm_vcpu_kick(vcpu);
+	}
+}
+
 int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
 {
 	unsigned long nr, a0, a1, a2, a3, ret;
@@ -5528,6 +5558,10 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
 	case KVM_HC_VAPIC_POLL_IRQ:
 		ret = 0;
 		break;
+	case KVM_HC_KICK_CPU:
+		kvm_pv_kick_cpu_op(vcpu->kvm, a0, a1);
+		ret = 0;
+		break;
 	default:
 		ret = -KVM_ENOSYS;
 		break;
@@ -5950,6 +5984,7 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
 				kvm_apic_accept_events(vcpu);
 				switch(vcpu->arch.mp_state) {
 				case KVM_MP_STATE_HALTED:
+					vcpu->arch.pv.pv_unhalted = false;
 					vcpu->arch.mp_state  						KVM_MP_STATE_RUNNABLE;
 				case KVM_MP_STATE_RUNNABLE:
@@ -6770,6 +6805,7 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
 	BUG_ON(vcpu->kvm == NULL);
 	kvm = vcpu->kvm;
 
+	vcpu->arch.pv.pv_unhalted = false;
 	vcpu->arch.emulate_ctxt.ops = &emulate_ops;
 	if (!irqchip_in_kernel(kvm) || kvm_vcpu_is_bsp(vcpu))
 		vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
@@ -7103,6 +7139,7 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
 		!vcpu->arch.apf.halted)
 		|| !list_empty_careful(&vcpu->async_pf.done)
 		|| kvm_apic_has_events(vcpu)
+		|| vcpu->arch.pv.pv_unhalted
 		|| atomic_read(&vcpu->arch.nmi_queued) ||
 		(kvm_arch_interrupt_allowed(vcpu) &&
 		 kvm_cpu_has_interrupt(vcpu));

kvm : Fold pv_unhalt flag into GET_MP_STATE ioctl to aid migration

From: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>

During migration, any vcpu that got kicked but did not become runnable
(still in halted state) should be runnable after migration.

Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
Acked-by: Gleb Natapov <gleb at redhat.com>
Acked-by: Ingo Molnar <mingo at kernel.org>
---
 arch/x86/kvm/x86.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index dae4575..1e73dab 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6284,7 +6284,12 @@ int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu
*vcpu,
 				    struct kvm_mp_state *mp_state)
 {
 	kvm_apic_accept_events(vcpu);
-	mp_state->mp_state = vcpu->arch.mp_state;
+	if (vcpu->arch.mp_state == KVM_MP_STATE_HALTED &&
+					vcpu->arch.pv.pv_unhalted)
+		mp_state->mp_state = KVM_MP_STATE_RUNNABLE;
+	else
+		mp_state->mp_state = vcpu->arch.mp_state;
+
 	return 0;
 }

kvm hypervisor: Simplify kvm_for_each_vcpu with kvm_irq_delivery_to_apic

From: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>

Note that we are using APIC_DM_REMRD which has reserved usage.
In future if APIC_DM_REMRD usage is standardized, then we should
find some other way or go back to old method.

Suggested-by: Gleb Natapov <gleb at redhat.com>
Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
Acked-by: Gleb Natapov <gleb at redhat.com>
Acked-by: Ingo Molnar <mingo at kernel.org>
---
 arch/x86/kvm/lapic.c |    5 ++++-
 arch/x86/kvm/x86.c   |   25 ++++++-------------------
 2 files changed, 10 insertions(+), 20 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index afc1124..48c13c9 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -706,7 +706,10 @@ out:
 		break;
 
 	case APIC_DM_REMRD:
-		apic_debug("Ignoring delivery mode 3\n");
+		result = 1;
+		vcpu->arch.pv.pv_unhalted = 1;
+		kvm_make_request(KVM_REQ_EVENT, vcpu);
+		kvm_vcpu_kick(vcpu);
 		break;
 
 	case APIC_DM_SMI:
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1e73dab..640d112 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5502,27 +5502,14 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
  */
 static void kvm_pv_kick_cpu_op(struct kvm *kvm, unsigned long flags, int
apicid)
 {
-	struct kvm_vcpu *vcpu = NULL;
-	int i;
+	struct kvm_lapic_irq lapic_irq;
 
-	kvm_for_each_vcpu(i, vcpu, kvm) {
-		if (!kvm_apic_present(vcpu))
-			continue;
+	lapic_irq.shorthand = 0;
+	lapic_irq.dest_mode = 0;
+	lapic_irq.dest_id = apicid;
 
-		if (kvm_apic_match_dest(vcpu, 0, 0, apicid, 0))
-			break;
-	}
-	if (vcpu) {
-		/*
-		 * Setting unhalt flag here can result in spurious runnable
-		 * state when unhalt reset does not happen in vcpu_block.
-		 * But that is harmless since that should soon result in halt.
-		 */
-		vcpu->arch.pv.pv_unhalted = true;
-		/* We need everybody see unhalt before vcpu unblocks */
-		smp_wmb();
-		kvm_vcpu_kick(vcpu);
-	}
+	lapic_irq.delivery_mode = APIC_DM_REMRD;
+	kvm_irq_delivery_to_apic(kvm, 0, &lapic_irq, NULL);
 }
 
 int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)

Documentation/kvm : Add documentation on Hypercalls and features used for PV
spinlock

From: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>

KVM_HC_KICK_CPU  hypercall added to wakeup halted vcpu in paravirtual spinlock
enabled guest.

KVM_FEATURE_PV_UNHALT enables guest to check whether pv spinlock can be enabled
in guest.

Thanks Vatsa for rewriting KVM_HC_KICK_CPU

Signed-off-by: Srivatsa Vaddagiri <vatsa at linux.vnet.ibm.com>
Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
Acked-by: Gleb Natapov <gleb at redhat.com>
Acked-by: Ingo Molnar <mingo at kernel.org>
---
 Documentation/virtual/kvm/cpuid.txt      |    4 ++++
 Documentation/virtual/kvm/hypercalls.txt |   14 ++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/Documentation/virtual/kvm/cpuid.txt
b/Documentation/virtual/kvm/cpuid.txt
index 83afe65..22ff659 100644
--- a/Documentation/virtual/kvm/cpuid.txt
+++ b/Documentation/virtual/kvm/cpuid.txt
@@ -43,6 +43,10 @@ KVM_FEATURE_CLOCKSOURCE2           ||     3 || kvmclock
available at msrs
 KVM_FEATURE_ASYNC_PF               ||     4 || async pf can be enabled by
                                    ||       || writing to msr 0x4b564d02
 ------------------------------------------------------------------------------
+KVM_FEATURE_PV_UNHALT              ||     7 || guest checks this feature bit
+                                   ||       || before enabling paravirtualized
+                                   ||       || spinlock support.
+------------------------------------------------------------------------------
 KVM_FEATURE_CLOCKSOURCE_STABLE_BIT ||    24 || host will warn if no guest-side
                                    ||       || per-cpu warps are expected in
                                    ||       || kvmclock.
diff --git a/Documentation/virtual/kvm/hypercalls.txt
b/Documentation/virtual/kvm/hypercalls.txt
index ea113b5..022198e 100644
--- a/Documentation/virtual/kvm/hypercalls.txt
+++ b/Documentation/virtual/kvm/hypercalls.txt
@@ -64,3 +64,17 @@ Purpose: To enable communication between the hypervisor and
guest there is a
 shared page that contains parts of supervisor visible register state.
 The guest can map this shared page to access its supervisor register through
 memory using this hypercall.
+
+5. KVM_HC_KICK_CPU
+------------------------
+Architecture: x86
+Status: active
+Purpose: Hypercall used to wakeup a vcpu from HLT state
+Usage example : A vcpu of a paravirtualized guest that is busywaiting in guest
+kernel mode for an event to occur (ex: a spinlock to become available) can
+execute HLT instruction once it has busy-waited for more than a threshold
+time-interval. Execution of HLT instruction would cause the hypervisor to put
+the vcpu to sleep until occurence of an appropriate event. Another vcpu of the
+same guest can wakeup the sleeping vcpu by issuing KVM_HC_KICK_CPU hypercall,
+specifying APIC ID (a1) of the vcpu to be woken up. An additional argument (a0)
+is used in the hypercall for future use.

On Tue, Aug 6, 2013 at 11:23 AM, Raghavendra K T
<raghavendra.kt at linux.vnet.ibm.com> wrote:
> kvm : Fold pv_unhalt flag into GET_MP_STATE ioctl to aid migration
>
> From: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
>
> During migration, any vcpu that got kicked but did not become runnable
> (still in halted state) should be runnable after migration.
If this is about migration correctness, could it get folded into the
previous patch 2/5, so that there's not a broken commit which could
hurt bisection?
>
> Signed-off-by: Raghavendra K T <raghavendra.kt at linux.vnet.ibm.com>
> Acked-by: Gleb Natapov <gleb at redhat.com>
> Acked-by: Ingo Molnar <mingo at kernel.org>
> ---
>  arch/x86/kvm/x86.c |    7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index dae4575..1e73dab 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6284,7 +6284,12 @@ int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu
*vcpu,
>                                     struct kvm_mp_state *mp_state)
>  {
>         kvm_apic_accept_events(vcpu);
> -       mp_state->mp_state = vcpu->arch.mp_state;
> +       if (vcpu->arch.mp_state == KVM_MP_STATE_HALTED &&
> +                                       vcpu->arch.pv.pv_unhalted)
> +               mp_state->mp_state = KVM_MP_STATE_RUNNABLE;
> +       else
> +               mp_state->mp_state = vcpu->arch.mp_state;
> +
>         return 0;
>  }
>
>
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