• Roman Kagan's avatar
    kvm: x86: hyperv: make VP_INDEX managed by userspace · d3457c87
    Roman Kagan authored
    Hyper-V identifies vCPUs by Virtual Processor Index, which can be
    queried via HV_X64_MSR_VP_INDEX msr.  It is defined by the spec as a
    sequential number which can't exceed the maximum number of vCPUs per VM.
    APIC ids can be sparse and thus aren't a valid replacement for VP
    Current KVM uses its internal vcpu index as VP_INDEX.  However, to make
    it predictable and persistent across VM migrations, the userspace has to
    control the value of VP_INDEX.
    This patch achieves that, by storing vp_index explicitly on vcpu, and
    allowing HV_X64_MSR_VP_INDEX to be set from the host side.  For
    compatibility it's initialized to KVM vcpu index.  Also a few variables
    are renamed to make clear distinction betweed this Hyper-V vp_index and
    KVM vcpu_id (== APIC id).  Besides, a new capability,
    KVM_CAP_HYPERV_VP_INDEX, is added to allow the userspace to skip
    attempting msr writes where unsupported, to avoid spamming error logs.
    Signed-off-by: default avatarRoman Kagan <rkagan@virtuozzo.com>
    Signed-off-by: default avatarRadim Krčmář <rkrcmar@redhat.com>
api.txt 143 KB