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KVM: x86: hyper-v: Allocate Hyper-V context lazily

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Hyper-V context is only needed for guests which use Hyper-V emulation in
KVM (e.g. Windows/Hyper-V guests) so we don't actually need to allocate
it in kvm_arch_vcpu_create(), we can postpone the action until Hyper-V
specific MSRs are accessed or SynIC is enabled.

Once allocated, let's keep the context alive for the lifetime of the vCPU
as an attempt to free it would require additional synchronization with
other vCPUs and normally it is not supposed to happen.

Note, Hyper-V style hypercall enablement is done by writing to
HV_X64_MSR_GUEST_OS_ID so we don't need to worry about allocating Hyper-V
context from kvm_hv_hypercall().

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210126134816.1880136-15-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Vitaly Kuznetsov
2021-01-26 14:48:15 +01:00
committed by Paolo Bonzini
parent 8f014550df
commit fc08b628d7
3 changed files with 27 additions and 19 deletions
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9
arch/x86/kvm/x86.c
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@@ -10083,12 +10083,9 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
vcpu->arch.pending_external_vector = -1;
vcpu->arch.preempted_in_kernel = false;
if (kvm_hv_vcpu_init(vcpu))
goto free_guest_fpu;
r = static_call(kvm_x86_vcpu_create)(vcpu);
if (r)
goto free_hv_vcpu;
goto free_guest_fpu;
vcpu->arch.arch_capabilities = kvm_get_arch_capabilities();
vcpu->arch.msr_platform_info = MSR_PLATFORM_INFO_CPUID_FAULT;
@@ -10099,8 +10096,6 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
vcpu_put(vcpu);
return 0;
free_hv_vcpu:
kvm_hv_vcpu_uninit(vcpu);
free_guest_fpu:
kvm_free_guest_fpu(vcpu);
free_user_fpu:
@@ -10124,8 +10119,6 @@ void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
{
struct kvm *kvm = vcpu->kvm;
kvm_hv_vcpu_postcreate(vcpu);
if (mutex_lock_killable(&vcpu->mutex))
return;
vcpu_load(vcpu);