• Roman Kagan's avatar
    kvm: x86: hyperv: add KVM_CAP_HYPERV_SYNIC2 · efc479e6
    Roman Kagan authored
    There is a flaw in the Hyper-V SynIC implementation in KVM: when message
    page or event flags page is enabled by setting the corresponding msr,
    KVM zeroes it out.  This is problematic because on migration the
    corresponding MSRs are loaded on the destination, so the content of
    those pages is lost.
    
    This went unnoticed so far because the only user of those pages was
    in-KVM hyperv synic timers, which could continue working despite that
    zeroing.
    
    Newer QEMU uses those pages for Hyper-V VMBus implementation, and
    zeroing them breaks the migration.
    
    Besides, in newer QEMU the content of those pages is fully managed by
    QEMU, so zeroing them is undesirable even when writing the MSRs from the
    guest side.
    
    To support this new scheme, introduce a new capability,
    KVM_CAP_HYPERV_SYNIC2, which, when enabled, makes sure that the synic
    pages aren't zeroed out in KVM.
    Signed-off-by: default avatarRoman Kagan <rkagan@virtuozzo.com>
    Signed-off-by: default avatarRadim Krčmář <rkrcmar@redhat.com>
    efc479e6
api.txt 143 KB