Re: [PATCH v2 06/15] kvm: x86: Add support for activate/de-activate APICv at runtime

[Vitaly Kuznetsov <vkuznets@redhat.com>]

"Suthikulpanit, Suravee" <Suravee.Suthikulpanit@amd.com> writes:

> Certain runtime conditions require APICv to be temporary deactivated.
> However, current implementation only support permanently deactivate
> APICv at runtime (mainly used when running Hyper-V guest).
>
> In addtion, for AMD, when activate / deactivate APICv during runtime,
> all vcpus in the VM has to be operating in the same APICv mode, which
> requires the requesting (main) vcpu to notify others.
>
> So, introduce interfaces to request all vcpus to activate/deactivate
> APICv.
>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> ---
>  arch/x86/include/asm/kvm_host.h |  9 +++++
>  arch/x86/kvm/x86.c              | 76 +++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 85 insertions(+)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 04d7066..dfb7c3d 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -76,6 +76,10 @@
>  #define KVM_REQ_HV_STIMER		KVM_ARCH_REQ(22)
>  #define KVM_REQ_LOAD_EOI_EXITMAP	KVM_ARCH_REQ(23)
>  #define KVM_REQ_GET_VMCS12_PAGES	KVM_ARCH_REQ(24)
> +#define KVM_REQ_APICV_ACTIVATE		\
> +	KVM_ARCH_REQ_FLAGS(25, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
> +#define KVM_REQ_APICV_DEACTIVATE	\
> +	KVM_ARCH_REQ_FLAGS(26, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
>  
>  #define CR0_RESERVED_BITS                                               \
>  	(~(unsigned long)(X86_CR0_PE | X86_CR0_MP | X86_CR0_EM | X86_CR0_TS \
> @@ -1089,6 +1093,7 @@ struct kvm_x86_ops {
>  	void (*enable_irq_window)(struct kvm_vcpu *vcpu);
>  	void (*update_cr8_intercept)(struct kvm_vcpu *vcpu, int tpr, int irr);
>  	bool (*get_enable_apicv)(struct kvm *kvm);
> +	void (*pre_update_apicv_exec_ctrl)(struct kvm_vcpu *vcpu, bool activate);
>  	void (*refresh_apicv_exec_ctrl)(struct kvm_vcpu *vcpu);
>  	void (*hwapic_irr_update)(struct kvm_vcpu *vcpu, int max_irr);
>  	void (*hwapic_isr_update)(struct kvm_vcpu *vcpu, int isr);
> @@ -1552,6 +1557,10 @@ int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low,
>  
>  void kvm_make_mclock_inprogress_request(struct kvm *kvm);
>  void kvm_make_scan_ioapic_request(struct kvm *kvm);
> +void kvm_vcpu_deactivate_apicv(struct kvm_vcpu *vcpu);
> +void kvm_vcpu_activate_apicv(struct kvm_vcpu *vcpu);
> +void kvm_make_apicv_activate_request(struct kvm_vcpu *vcpu);
> +void kvm_make_apicv_deactivate_request(struct kvm_vcpu *vcpu, bool disable);
>  
>  void kvm_arch_async_page_not_present(struct kvm_vcpu *vcpu,
>  				     struct kvm_async_pf *work);
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index f9c3f63..40a20bf 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -26,6 +26,7 @@
>  #include "cpuid.h"
>  #include "pmu.h"
>  #include "hyperv.h"
> +#include "lapic.h"
>  
>  #include <linux/clocksource.h>
>  #include <linux/interrupt.h>
> @@ -7163,6 +7164,22 @@ static void kvm_pv_kick_cpu_op(struct kvm *kvm, unsigned long flags, int apicid)
>  	kvm_irq_delivery_to_apic(kvm, NULL, &lapic_irq, NULL);
>  }
>  
> +void kvm_vcpu_activate_apicv(struct kvm_vcpu *vcpu)
> +{
> +	if (!lapic_in_kernel(vcpu)) {
> +		WARN_ON_ONCE(!vcpu->arch.apicv_active);
> +		return;
> +	}
> +	if (vcpu->arch.apicv_active)
> +		return;
> +
> +	vcpu->arch.apicv_active = true;
> +	kvm_apic_update_apicv(vcpu);
> +
> +	kvm_x86_ops->refresh_apicv_exec_ctrl(vcpu);
> +}
> +EXPORT_SYMBOL_GPL(kvm_vcpu_activate_apicv);
> +
>  void kvm_vcpu_deactivate_apicv(struct kvm_vcpu *vcpu)
>  {
>  	if (!lapic_in_kernel(vcpu)) {
> @@ -7173,8 +7190,11 @@ void kvm_vcpu_deactivate_apicv(struct kvm_vcpu *vcpu)
>  		return;
>  
>  	vcpu->arch.apicv_active = false;
> +	kvm_apic_update_apicv(vcpu);
> +
>  	kvm_x86_ops->refresh_apicv_exec_ctrl(vcpu);
>  }
> +EXPORT_SYMBOL_GPL(kvm_vcpu_deactivate_apicv);
>  
>  int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
>  {
> @@ -7668,6 +7688,58 @@ void kvm_make_scan_ioapic_request(struct kvm *kvm)
>  	kvm_make_all_cpus_request(kvm, KVM_REQ_SCAN_IOAPIC);
>  }
>  
> +void kvm_make_apicv_activate_request(struct kvm_vcpu *vcpu)
> +{
> +	int i;
> +	struct kvm_vcpu *v;
> +	struct kvm *kvm = vcpu->kvm;
> +
> +	mutex_lock(&kvm->arch.apicv_lock);
> +	if (kvm->arch.apicv_state != APICV_DEACTIVATED) {
> +		mutex_unlock(&kvm->arch.apicv_lock);
> +		return;
> +	}
> +
> +	kvm_for_each_vcpu(i, v, kvm)
> +		kvm_clear_request(KVM_REQ_APICV_DEACTIVATE, v);
> +
> +	if (kvm_x86_ops->pre_update_apicv_exec_ctrl)
> +		kvm_x86_ops->pre_update_apicv_exec_ctrl(vcpu, true);
> +
> +	kvm->arch.apicv_state = APICV_ACTIVATED;
> +
> +	kvm_make_all_cpus_request(kvm, KVM_REQ_APICV_ACTIVATE);
> +
> +	mutex_unlock(&kvm->arch.apicv_lock);
> +}
> +EXPORT_SYMBOL_GPL(kvm_make_apicv_activate_request);
> +
> +void kvm_make_apicv_deactivate_request(struct kvm_vcpu *vcpu, bool disable)
> +{
> +	int i;
> +	struct kvm_vcpu *v;
> +	struct kvm *kvm = vcpu->kvm;
> +
> +	mutex_lock(&kvm->arch.apicv_lock);
> +	if (kvm->arch.apicv_state == APICV_DEACTIVATED) {
> +		mutex_unlock(&kvm->arch.apicv_lock);
> +		return;
> +	}
> +
> +	kvm_for_each_vcpu(i, v, kvm)
> +		kvm_clear_request(KVM_REQ_APICV_ACTIVATE, v);

Could you please elaborate on when we need to eat the
KVM_REQ_APICV_ACTIVATE request here (and KVM_REQ_APICV_DEACTIVATE in
kvm_make_apicv_activate_request() respectively)? To me, this looks like
a possible source of hard-to-debug problems in the future.

> +
> +	if (kvm_x86_ops->pre_update_apicv_exec_ctrl)
> +		kvm_x86_ops->pre_update_apicv_exec_ctrl(vcpu, false);
> +
> +	kvm->arch.apicv_state = disable ? APICV_DISABLED : APICV_DEACTIVATED;
> +
> +	kvm_make_all_cpus_request(kvm, KVM_REQ_APICV_DEACTIVATE);
> +
> +	mutex_unlock(&kvm->arch.apicv_lock);
> +}
> +EXPORT_SYMBOL_GPL(kvm_make_apicv_deactivate_request);
> +
>  static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
>  {
>  	if (!kvm_apic_present(vcpu))
> @@ -7854,6 +7926,10 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  		 */
>  		if (kvm_check_request(KVM_REQ_HV_STIMER, vcpu))
>  			kvm_hv_process_stimers(vcpu);
> +		if (kvm_check_request(KVM_REQ_APICV_ACTIVATE, vcpu))
> +			kvm_vcpu_activate_apicv(vcpu);
> +		if (kvm_check_request(KVM_REQ_APICV_DEACTIVATE, vcpu))
> +			kvm_vcpu_deactivate_apicv(vcpu);
>  	}
>  
>  	if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) {

-- 
Vitaly