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    Subject[PATCH AUTOSEL 4.19 013/167] KVM: x86: hyperv: keep track of mismatched VP indexes
    Date
    From: Vitaly Kuznetsov <vkuznets@redhat.com>

    [ Upstream commit 87ee613d076351950b74383215437f841ebbeb75 ]

    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@redhat.com>
    Reviewed-by: Roman Kagan <rkagan@virtuozzo.com>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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 3245b95ad2d97..b6417454a9d79 100644
    --- a/arch/x86/include/asm/kvm_host.h
    +++ b/arch/x86/include/asm/kvm_host.h
    @@ -784,6 +784,9 @@ 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 3f2775aac5545..2bb554b90b3c2 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;
    +
    + /*
    + * The VP index is initialized to vcpu_index by
    + * kvm_hv_vcpu_postcreate so they initially match. Now the
    + * VP index is changing, adjust num_mismatched_vp_indexes if
    + * it now matches or no longer matches 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;
    --
    2.20.1
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