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KVM: x86: hyper-v: Deactivate APICv only when AutoEOI feature is in use

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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: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210810205251.424103-12-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Vitaly Kuznetsov 2021-08-10 23:52:46 +03:00 committed by Paolo Bonzini
parent 4628efcd4e
commit 0f250a6463
2 changed files with 32 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
arch/x86/include/asm/kvm_host.h
View File

@ -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;
};

32
arch/x86/kvm/hyperv.c
View File

@ -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.