Roman Kagan <rkagan@xxxxxxxxxxxxx> writes:
> 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.
>
Of course, yes, will update the comment in case I'll be re-submitting.
>> + */
>> + 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>
Thanks!
--
Vitaly
