Trapping blocking WFE is extremely beneficial in situations where
the system is oversubscribed, as it allows another thread to run
while being blocked. In a non-oversubscribed environment, this is
the complete opposite, and trapping WFE is just unnecessary overhead.
Let's only enable WFE trapping if the CPU has more than a single task
to run (that is, more than just the vcpu thread).
Reviewed-by: Christoffer Dall <christoffer.dall@xxxxxxx>
Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
---
arch/arm/include/asm/kvm_emulate.h | 10 ++++++++++
arch/arm64/include/asm/kvm_emulate.h | 10 ++++++++++
virt/kvm/arm/arm.c | 6 ++++++
3 files changed, 26 insertions(+)
diff --git a/arch/arm/include/asm/kvm_emulate.h b/arch/arm/include/asm/kvm_emulate.h
index 6493bd479ddc..b50fe8380868 100644
--- a/arch/arm/include/asm/kvm_emulate.h
+++ b/arch/arm/include/asm/kvm_emulate.h
@@ -107,6 +107,16 @@ static inline unsigned long *vcpu_hcr(const struct kvm_vcpu *vcpu)
return (unsigned long *)&vcpu->arch.hcr;
}
+static inline void vcpu_clear_wfe_traps(struct kvm_vcpu *vcpu)
+{
+ vcpu->arch.hcr &= ~HCR_TWE;
+}
+
+static inline void vcpu_set_wfe_traps(struct kvm_vcpu *vcpu)
+{
+ vcpu->arch.hcr |= HCR_TWE;
+}
+
static inline bool vcpu_mode_is_32bit(const struct kvm_vcpu *vcpu)
{
return 1;
diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index dd98fdf33d99..bfefdd9a72eb 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -83,6 +83,16 @@ static inline unsigned long *vcpu_hcr(struct kvm_vcpu *vcpu)
return (unsigned long *)&vcpu->arch.hcr_el2;
}
+static inline void vcpu_clear_wfe_traps(struct kvm_vcpu *vcpu)
+{
+ vcpu->arch.hcr_el2 &= ~HCR_TWE;
+}
+
+static inline void vcpu_set_wfe_traps(struct kvm_vcpu *vcpu)
+{
+ vcpu->arch.hcr_el2 |= HCR_TWE;
+}
+
static inline void vcpu_set_vsesr(struct kvm_vcpu *vcpu, u64 vsesr)
{
vcpu->arch.vsesr_el2 = vsesr;
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index 04e554cae3a2..8e66b89a3db2 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -30,6 +30,7 @@
#include <linux/kvm.h>
#include <linux/kvm_irqfd.h>
#include <linux/irqbypass.h>
+#include <linux/sched/stat.h>
#include <trace/events/kvm.h>
#include <kvm/arm_pmu.h>
#include <kvm/arm_psci.h>
@@ -380,6 +381,11 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
kvm_timer_vcpu_load(vcpu);
kvm_vcpu_load_sysregs(vcpu);
kvm_arch_vcpu_load_fp(vcpu);
+
+ if (single_task_running())
+ vcpu_clear_wfe_traps(vcpu);
+ else
+ vcpu_set_wfe_traps(vcpu);
}
void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
--
2.18.0
