[PATCH v3 07/26] KVM: VMX: Move preemption timer <=> hrtimer dance to common x86

Sean Christopherson
2021-12-08T01:55:45Z

Handle the switch to/from the hypervisor/software timer when a vCPU is
blocking in common x86 instead of in VMX. Even though VMX is the only
user of a hypervisor timer, the logic and all functions involved are
generic x86 (unless future CPUs do something completely different and
implement a hypervisor timer that runs regardless of mode).

Handling the switch in common x86 will allow for the elimination of the
pre/post_blocks hooks, and also lets KVM switch back to the hypervisor
timer if and only if it was in use (without additional params). Add a
comment explaining why the switch cannot be deferred to kvm_sched_out()
or kvm_vcpu_block().

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
---
arch/x86/kvm/vmx/vmx.c | 6 +-----
arch/x86/kvm/x86.c | 21 +++++++++++++++++++++
2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 64932cc3e4e8..a5ba9a069f5d 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7444,16 +7444,12 @@ void vmx_update_cpu_dirty_logging(struct kvm_vcpu *vcpu)

static int vmx_pre_block(struct kvm_vcpu *vcpu)
{
- if (kvm_lapic_hv_timer_in_use(vcpu))
- kvm_lapic_switch_to_sw_timer(vcpu);
-
return 0;
}

static void vmx_post_block(struct kvm_vcpu *vcpu)
{
- if (kvm_x86_ops.set_hv_timer)
- kvm_lapic_switch_to_hv_timer(vcpu);
+
}

static void vmx_setup_mce(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a05a26471f19..f13a61830d9d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10041,8 +10041,21 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)

static inline int vcpu_block(struct kvm *kvm, struct kvm_vcpu *vcpu)
{
+ bool hv_timer;
+
if (!kvm_arch_vcpu_runnable(vcpu) &&
(!kvm_x86_ops.pre_block || static_call(kvm_x86_pre_block)(vcpu) == 0)) {
+ /*
+ * Switch to the software timer before halt-polling/blocking as
+ * the guest's timer may be a break event for the vCPU, and the
+ * hypervisor timer runs only when the CPU is in guest mode.
+ * Switch before halt-polling so that KVM recognizes an expired
+ * timer before blocking.
+ */
+ hv_timer = kvm_lapic_hv_timer_in_use(vcpu);
+ if (hv_timer)
+ kvm_lapic_switch_to_sw_timer(vcpu);
+
srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
if (vcpu->arch.mp_state == KVM_MP_STATE_HALTED)
kvm_vcpu_halt(vcpu);
@@ -10050,6 +10063,9 @@ static inline int vcpu_block(struct kvm *kvm, struct kvm_vcpu *vcpu)
kvm_vcpu_block(vcpu);
vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);

+ if (hv_timer)
+ kvm_lapic_switch_to_hv_timer(vcpu);
+
if (kvm_x86_ops.post_block)
static_call(kvm_x86_post_block)(vcpu);

@@ -10244,6 +10260,11 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
r = -EINTR;
goto out;
}
+ /*
+ * It should be impossible for the hypervisor timer to be in
+ * use before KVM has ever run the vCPU.
+ */
+ WARN_ON_ONCE(kvm_lapic_hv_timer_in_use(vcpu));
kvm_vcpu_block(vcpu);
if (kvm_apic_accept_events(vcpu) < 0) {
r = 0;
--
2.34.1.400.ga245620fadb-goog