[PATCH v2 2/4] KVM: X86: implement the logic for spinlock optimization

Longpeng(Mike)
2017-08-08T04:05:33Z

1. Implements the kvm_arch_vcpu_in_kernel(), because get_cpl requires
vcpu_load, so we must cache the result(whether the vcpu was preempted
when its cpl=0) in kvm_vcpu_arch.

2. Add ->spin_in_kernel hook, because we can get benefit from VMX.

Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com>
---
arch/x86/include/asm/kvm_host.h | 5 +++++
arch/x86/kvm/hyperv.c | 2 +-
arch/x86/kvm/svm.c | 8 +++++++-
arch/x86/kvm/vmx.c | 16 +++++++++++++++-
arch/x86/kvm/x86.c | 7 ++++++-
5 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 87ac4fb..d2b2d57 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -688,6 +688,9 @@ struct kvm_vcpu_arch {

/* GPA available (AMD only) */
bool gpa_available;
+
+ /* be preempted when it's in kernel-mode(cpl=0) */
+ bool preempted_in_kernel;
};

struct kvm_lpage_info {
@@ -1057,6 +1060,8 @@ struct kvm_x86_ops {
void (*cancel_hv_timer)(struct kvm_vcpu *vcpu);

void (*setup_mce)(struct kvm_vcpu *vcpu);
+
+ bool (*spin_in_kernel)(struct kvm_vcpu *vcpu);
};

struct kvm_arch_async_pf {
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index cd0e6e6..dec5e8a 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -1268,7 +1268,7 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)

switch (code) {
case HVCALL_NOTIFY_LONG_SPIN_WAIT:
- kvm_vcpu_on_spin(vcpu, kvm_arch_vcpu_in_kernel(vcpu));
+ kvm_vcpu_on_spin(vcpu, kvm_x86_ops->spin_in_kernel(vcpu));
break;
case HVCALL_POST_MESSAGE:
case HVCALL_SIGNAL_EVENT:
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index e6ed24e..ccb6df7 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -3751,7 +3751,7 @@ static int pause_interception(struct vcpu_svm *svm)
{
struct kvm_vcpu *vcpu = &(svm->vcpu);

- kvm_vcpu_on_spin(vcpu, kvm_arch_vcpu_in_kernel(vcpu));
+ kvm_vcpu_on_spin(vcpu, kvm_x86_ops->spin_in_kernel(vcpu));
return 1;
}

@@ -5364,6 +5364,11 @@ static void svm_setup_mce(struct kvm_vcpu *vcpu)
vcpu->arch.mcg_cap &= 0x1ff;
}

+static bool svm_spin_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return svm_get_cpl(vcpu) == 0;
+}
+
static struct kvm_x86_ops svm_x86_ops __ro_after_init = {
.cpu_has_kvm_support = has_svm,
.disabled_by_bios = is_disabled,
@@ -5476,6 +5481,7 @@ static void svm_setup_mce(struct kvm_vcpu *vcpu)
.deliver_posted_interrupt = svm_deliver_avic_intr,
.update_pi_irte = svm_update_pi_irte,
.setup_mce = svm_setup_mce,
+ .spin_in_kernel = svm_spin_in_kernel,
};

static int __init svm_init(void)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 9d6223a..297a158 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -6761,7 +6761,8 @@ static int handle_pause(struct kvm_vcpu *vcpu)
if (ple_gap)
grow_ple_window(vcpu);

- kvm_vcpu_on_spin(vcpu, kvm_arch_vcpu_in_kernel(vcpu));
+ /* See comments in vmx_spin_in_kernel() */
+ kvm_vcpu_on_spin(vcpu, true);
return kvm_skip_emulated_instruction(vcpu);
}

@@ -11636,6 +11637,17 @@ static void vmx_setup_mce(struct kvm_vcpu *vcpu)
~FEATURE_CONTROL_LMCE;
}

+static bool vmx_spin_in_kernel(struct kvm_vcpu *vcpu)
+{
+ /*
+ * Intel sdm vol3 ch-25.1.3 says: The “PAUSE-loop exiting”
+ * VM-execution control is ignored if CPL > 0. OTOH, KVM
+ * never set PAUSE_EXITING and just set PLE if supported,
+ * so the vcpu must be CPL=0 if it gets a PAUSE exit.
+ */
+ return true;
+}
+
static struct kvm_x86_ops vmx_x86_ops __ro_after_init = {
.cpu_has_kvm_support = cpu_has_kvm_support,
.disabled_by_bios = vmx_disabled_by_bios,
@@ -11763,6 +11775,8 @@ static void vmx_setup_mce(struct kvm_vcpu *vcpu)
#endif

.setup_mce = vmx_setup_mce,
+
+ .spin_in_kernel = vmx_spin_in_kernel,
};

static int __init vmx_init(void)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4430be6..28299b9 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2881,6 +2881,10 @@ static void kvm_steal_time_set_preempted(struct kvm_vcpu *vcpu)
void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
{
int idx;
+
+ if (vcpu->preempted)
+ vcpu->arch.preempted_in_kernel = !kvm_x86_ops->get_cpl(vcpu);
+
/*
* Disable page faults because we're in atomic context here.
* kvm_write_guest_offset_cached() would call might_fault()
@@ -7992,6 +7996,7 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
kvm_pmu_init(vcpu);

vcpu->arch.pending_external_vector = -1;
+ vcpu->arch.preempted_in_kernel = false;

kvm_hv_vcpu_init(vcpu);

@@ -8441,7 +8446,7 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)

bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu)
{
- return false;
+ return vcpu->arch.preempted_in_kernel;
}
EXPORT_SYMBOL_GPL(kvm_arch_vcpu_in_kernel);

--
1.8.3.1