[PATCH 3/3] KVM: nVMX: Migrate the VMX-preemption timer

Jim Mattson
2020-05-08T20:37:07Z

The hrtimer used to emulate the VMX-preemption timer must be pinned to
the same logical processor as the vCPU thread to be interrupted if we
want to have any hope of adhering to the architectural specification
of the VMX-preemption timer. Even with this change, the emulated
VMX-preemption timer VM-exit occasionally arrives too late.

Signed-off-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Peter Shier <pshier@google.com>
Reviewed-by: Oliver Upton <oupton@google.com>
---
arch/x86/include/asm/kvm_host.h | 2 ++
arch/x86/kvm/irq.c | 2 ++
arch/x86/kvm/vmx/vmx.c | 11 +++++++++++
3 files changed, 15 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 42a2d0d3984a..a47c71d13039 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1254,6 +1254,8 @@ struct kvm_x86_ops {

bool (*apic_init_signal_blocked)(struct kvm_vcpu *vcpu);
int (*enable_direct_tlbflush)(struct kvm_vcpu *vcpu);
+
+ void (*migrate_timers)(struct kvm_vcpu *vcpu);
};

struct kvm_x86_init_ops {
diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c
index e330e7d125f7..54f7ea68083b 100644
--- a/arch/x86/kvm/irq.c
+++ b/arch/x86/kvm/irq.c
@@ -159,6 +159,8 @@ void __kvm_migrate_timers(struct kvm_vcpu *vcpu)
{
__kvm_migrate_apic_timer(vcpu);
__kvm_migrate_pit_timer(vcpu);
+ if (kvm_x86_ops.migrate_timers)
+ kvm_x86_ops.migrate_timers(vcpu);
}

bool kvm_arch_irqfd_allowed(struct kvm *kvm, struct kvm_irqfd *args)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index c2c6335a998c..3896dea72082 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7687,6 +7687,16 @@ static bool vmx_apic_init_signal_blocked(struct kvm_vcpu *vcpu)
return to_vmx(vcpu)->nested.vmxon;
}

+static void vmx_migrate_timers(struct kvm_vcpu *vcpu)
+{
+ if (is_guest_mode(vcpu)) {
+ struct hrtimer *timer = &to_vmx(vcpu)->nested.preemption_timer;
+
+ if (hrtimer_try_to_cancel(timer) == 1)
+ hrtimer_start_expires(timer, HRTIMER_MODE_ABS_PINNED);
+ }
+}
+
static void hardware_unsetup(void)
{
if (nested)
@@ -7838,6 +7848,7 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
.nested_get_evmcs_version = NULL,
.need_emulation_on_page_fault = vmx_need_emulation_on_page_fault,
.apic_init_signal_blocked = vmx_apic_init_signal_blocked,
+ .migrate_timers = vmx_migrate_timers,
};

static __init int hardware_setup(void)
--
2.26.2.645.ge9eca65c58-goog