Currently, the only eVMCS version, supported by KVM (and described in TLFS) is '1'. When Enlightened VMCS feature is enabled, QEMU takes the supported eVMCS version range (from KVM_CAP_HYPERV_ENLIGHTENED_VMCS enablement) and puts it to guest visible CPUIDs. When (and if) eVMCS ver.2 appears a problem on migration is expected: it doesn't seem to be possible to migrate from a host supporting eVMCS ver.2 to a host, which only support eVMCS ver.1.
Hardcode eVMCS ver.1 as the result of 'hv-evmcs' enablement for now. Newer eVMCS versions will have to have their own enablement options (e.g. 'hv-evmcs=2'). Signed-off-by: Vitaly Kuznetsov <vkuzn...@redhat.com> --- docs/hyperv.txt | 2 +- target/i386/kvm/kvm.c | 16 +++++++++++----- 2 files changed, 12 insertions(+), 6 deletions(-) diff --git a/docs/hyperv.txt b/docs/hyperv.txt index a51953daa833..000638a2fd38 100644 --- a/docs/hyperv.txt +++ b/docs/hyperv.txt @@ -170,7 +170,7 @@ Recommended: hv-frequencies 3.16. hv-evmcs =============== The enlightenment is nested specific, it targets Hyper-V on KVM guests. When -enabled, it provides Enlightened VMCS feature to the guest. The feature +enabled, it provides Enlightened VMCS version 1 feature to the guest. The feature implements paravirtualized protocol between L0 (KVM) and L1 (Hyper-V) hypervisors making L2 exits to the hypervisor faster. The feature is Intel-only. Note: some virtualization features (e.g. Posted Interrupts) are disabled when diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c index c676ee8b38a7..d57eede5dc81 100644 --- a/target/i386/kvm/kvm.c +++ b/target/i386/kvm/kvm.c @@ -1490,13 +1490,19 @@ static int hyperv_init_vcpu(X86CPU *cpu) ret = kvm_vcpu_enable_cap(cs, KVM_CAP_HYPERV_ENLIGHTENED_VMCS, 0, (uintptr_t)&evmcs_version); - if (ret < 0) { - fprintf(stderr, "Hyper-V %s is not supported by kernel\n", - kvm_hyperv_properties[HYPERV_FEAT_EVMCS].desc); + /* + * KVM is required to support EVMCS ver.1. as that's what 'hv-evmcs' + * option sets. Note: we hardcode the maximum supported eVMCS version + * to '1' as well so 'hv-evmcs' feature is migratable even when (and if) + * ver.2 is implemented. A new option (e.g. 'hv-evmcs=2') will then have + * to be added. + */ + if (ret < 0 || (uint8_t)evmcs_version > 1) { + error_report("Hyper-V %s verson 1 is not supported by kernel", + kvm_hyperv_properties[HYPERV_FEAT_EVMCS].desc); return ret; } - - cpu->hyperv_nested[0] = evmcs_version; + cpu->hyperv_nested[0] = (1 << 8) | 1; } return 0; -- 2.31.1