On Wed, Sep 26, 2018 at 07:02:56PM +0200, Vitaly Kuznetsov wrote:
> In most common cases VP index of a vcpu matches its vcpu index. Userspace
> is, however, free to set any mapping it wishes and we need to account for
> that when we need to find a vCPU with a particular VP index. To keep search
> algorithms optimal in both cases introduce 'num_mismatched_vp_indexes'
> counter showing how many vCPUs with mismatching VP index we have. In case
> the counter is zero we can assume vp_index == vcpu_idx.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> ---
> arch/x86/include/asm/kvm_host.h | 3 +++
> arch/x86/kvm/hyperv.c | 26 +++++++++++++++++++++++---
> 2 files changed, 26 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 09b2e3e2cf1b..711f79f1b5e6 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -781,6 +781,9 @@ struct kvm_hv {
> u64 hv_reenlightenment_control;
> u64 hv_tsc_emulation_control;
> u64 hv_tsc_emulation_status;
> +
> + /* How many vCPUs have VP index != vCPU index */
> + atomic_t num_mismatched_vp_indexes;
> };
>
> enum kvm_irqchip_mode {
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index c8764faf783b..6a19c8e3c432 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -1045,11 +1045,31 @@ static int kvm_hv_set_msr(struct kvm_vcpu *vcpu, u32 msr, u64 data, bool host)
> struct kvm_vcpu_hv *hv_vcpu = &vcpu->arch.hyperv;
>
> switch (msr) {
> - case HV_X64_MSR_VP_INDEX:
> - if (!host || (u32)data >= KVM_MAX_VCPUS)
> + case HV_X64_MSR_VP_INDEX: {
> + struct kvm_hv *hv = &vcpu->kvm->arch.hyperv;
> + int vcpu_idx = kvm_vcpu_get_idx(vcpu);
> + u32 new_vp_index = (u32)data;
> +
> + if (!host || new_vp_index >= KVM_MAX_VCPUS)
> return 1;
> - hv_vcpu->vp_index = (u32)data;
> +
> + if (new_vp_index == hv_vcpu->vp_index)
> + return 0;
> +
> + /*
> + * VP index is changing, increment num_mismatched_vp_indexes in
> + * case it was equal to vcpu_idx before; on the other hand, if
> + * the new VP index matches vcpu_idx num_mismatched_vp_indexes
> + * needs to be decremented.
It may be worth mentioning that the initial balance is provided by
kvm_hv_vcpu_postcreate setting vp_index = vcpu_idx.
> + */
> + if (hv_vcpu->vp_index == vcpu_idx)
> + atomic_inc(&hv->num_mismatched_vp_indexes);
> + else if (new_vp_index == vcpu_idx)
> + atomic_dec(&hv->num_mismatched_vp_indexes);
> +
> + hv_vcpu->vp_index = new_vp_index;
> break;
> + }
> case HV_X64_MSR_VP_ASSIST_PAGE: {
> u64 gfn;
> unsigned long addr;
Reviewed-by: Roman Kagan <rkagan@xxxxxxxxxxxxx>
