Commit 0f250a64 authored by Vitaly Kuznetsov's avatar Vitaly Kuznetsov Committed by Paolo Bonzini
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KVM: x86: hyper-v: Deactivate APICv only when AutoEOI feature is in use 



APICV_INHIBIT_REASON_HYPERV is currently unconditionally forced upon
SynIC activation as SynIC's AutoEOI is incompatible with APICv/AVIC. It is,
however, possible to track whether the feature was actually used by the
guest and only inhibit APICv/AVIC when needed.

TLFS suggests a dedicated 'HV_DEPRECATING_AEOI_RECOMMENDED' flag to let
Windows know that AutoEOI feature should be avoided. While it's up to
KVM userspace to set the flag, KVM can help a bit by exposing global
APICv/AVIC enablement.

Maxim:
   - always set HV_DEPRECATING_AEOI_RECOMMENDED in kvm_get_hv_cpuid,
     since this feature can be used regardless of AVIC

Paolo:
   - use arch.apicv_update_lock to protect the hv->synic_auto_eoi_used
     instead of atomic ops

Signed-off-by: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: default avatarMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210810205251.424103-12-mlevitsk@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 4628efcd

arch/x86/include/asm/kvm_host.h

+6 −0
Original line number Diff line number Diff line
@@ -981,6 +981,12 @@ struct kvm_hv { 
	/* How many vCPUs have VP index != vCPU index */

	atomic_t num_mismatched_vp_indexes;



	/*

	 * How many SynICs use 'AutoEOI' feature

	 * (protected by arch.apicv_update_lock)

	 */

	unsigned int synic_auto_eoi_used;



	struct hv_partition_assist_pg *hv_pa_pg;

	struct kvm_hv_syndbg hv_syndbg;

};

arch/x86/kvm/hyperv.c

+26 −6
Original line number Diff line number Diff line
@@ -88,6 +88,10 @@ static bool synic_has_vector_auto_eoi(struct kvm_vcpu_hv_synic *synic, 
static void synic_update_vector(struct kvm_vcpu_hv_synic *synic,

				int vector)

{

	struct kvm_vcpu *vcpu = hv_synic_to_vcpu(synic);

	struct kvm_hv *hv = to_kvm_hv(vcpu->kvm);

	int auto_eoi_old, auto_eoi_new;



	if (vector < HV_SYNIC_FIRST_VALID_VECTOR)

		return;
@@ -96,10 +100,30 @@ static void synic_update_vector(struct kvm_vcpu_hv_synic *synic, 
	else

		__clear_bit(vector, synic->vec_bitmap);



	auto_eoi_old = bitmap_weight(synic->auto_eoi_bitmap, 256);



	if (synic_has_vector_auto_eoi(synic, vector))

		__set_bit(vector, synic->auto_eoi_bitmap);

	else

		__clear_bit(vector, synic->auto_eoi_bitmap);



	auto_eoi_new = bitmap_weight(synic->auto_eoi_bitmap, 256);



	if (!!auto_eoi_old == !!auto_eoi_new)

		return;



	mutex_lock(&vcpu->kvm->arch.apicv_update_lock);



	if (auto_eoi_new)

		hv->synic_auto_eoi_used++;

	else

		hv->synic_auto_eoi_used--;



	__kvm_request_apicv_update(vcpu->kvm,

				   !hv->synic_auto_eoi_used,

				   APICV_INHIBIT_REASON_HYPERV);



	mutex_unlock(&vcpu->kvm->arch.apicv_update_lock);

}



static int synic_set_sint(struct kvm_vcpu_hv_synic *synic, int sint,
@@ -933,12 +957,6 @@ int kvm_hv_activate_synic(struct kvm_vcpu *vcpu, bool dont_zero_synic_pages) 


	synic = to_hv_synic(vcpu);



	/*

	 * Hyper-V SynIC auto EOI SINT's are

	 * not compatible with APICV, so request

	 * to deactivate APICV permanently.

	 */

	kvm_request_apicv_update(vcpu->kvm, false, APICV_INHIBIT_REASON_HYPERV);

	synic->active = true;

	synic->dont_zero_synic_pages = dont_zero_synic_pages;

	synic->control = HV_SYNIC_CONTROL_ENABLE;
@@ -2476,6 +2494,8 @@ int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid, 
				ent->eax |= HV_X64_ENLIGHTENED_VMCS_RECOMMENDED;

			if (!cpu_smt_possible())

				ent->eax |= HV_X64_NO_NONARCH_CORESHARING;



			ent->eax |= HV_DEPRECATING_AEOI_RECOMMENDED;

			/*

			 * Default number of spinlock retry attempts, matches

			 * HyperV 2016.