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Subject[PATCH 2/3] KVM: X86: implement the logic for spinlock optimization
Date
Implements the kvm_arch_vcpu_spin/preempt_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_arch_vcpu.

Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com>
---
arch/x86/include/asm/kvm_host.h | 5 +++++
arch/x86/kvm/svm.c | 6 ++++++
arch/x86/kvm/vmx.c | 20 ++++++++++++++++++++
arch/x86/kvm/x86.c | 9 +++++++--
4 files changed, 38 insertions(+), 2 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/svm.c b/arch/x86/kvm/svm.c
index 4d8141e..552ab4c 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -5352,6 +5352,11 @@ 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,
@@ -5464,6 +5469,7 @@ 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 39a6222..d0dfe2e 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -11547,6 +11547,25 @@ static void vmx_setup_mce(struct kvm_vcpu *vcpu)
~FEATURE_CONTROL_LMCE;
}

+static bool vmx_spin_in_kernel(struct kvm_vcpu *vcpu)
+{
+ u32 secondary_exec_ctrl = 0;
+
+ /*
+ * Intel sdm vol3 ch-25.1.3 says: The “PAUSE-loop exiting”
+ * VM-execution control is ignored if CPL > 0. So the vcpu
+ * is always exiting with CPL=0 if it uses PLE.
+ *
+ * The following block needs less cycles than vmx_get_cpl().
+ */
+ if (cpu_has_secondary_exec_ctrls())
+ secondary_exec_ctrl = vmcs_read32(SECONDARY_VM_EXEC_CONTROL);
+ if (secondary_exec_ctrl & SECONDARY_EXEC_PAUSE_LOOP_EXITING)
+ return true;
+
+ return vmx_get_cpl(vcpu) == 0;
+}
+
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,
@@ -11674,6 +11693,7 @@ 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 04c6a1f..fa79a60 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()
@@ -7988,6 +7992,7 @@ 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);

@@ -8437,12 +8442,12 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)

bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
{
- return false;
+ return kvm_x86_ops->spin_in_kernel(vcpu);
}

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

int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
--
1.8.3.1

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