On Wed, Mar 28, 2018 at 06:30:24PM +0300, Roman Kagan wrote:
> In order to guarantee compatibility on migration, QEMU should have
> complete control over the features it announces to the guest via CPUID.
>
> However, for a number of Hyper-V-related cpu properties, if the
> corresponding feature is not supported by the underlying KVM, the
> propery is silently ignored and the feature is not announced to the
> guest.
>
> Refuse to start with an error instead.
>
> Signed-off-by: Roman Kagan <rka...@virtuozzo.com>
Something I didn't consider before:
Will this block migration before it even starts, or will crash
the VM only after all migration data was sent to the destination?
I didn't test it, but kvm_arch_init_vcpu() seems to be too late
to block an invalid/unsupport configuration.
Maybe we can simply call hyperv_handle_properties() earlier,
inside x86_cpu_realizefn()?
(I know it's very late for this kind of intrusive change in
v2.12, but I still think it's a good idea to fix this as soon as
possible.)
> ---
> v1 -> v2:
> - indicate what flag requested the feature that can't be enabled in the
> error message
> - fix a typo in the error message for VP_RUNTIME
>
> target/i386/kvm.c | 32 ++++++++++++++++++++++++++++----
> 1 file changed, 28 insertions(+), 4 deletions(-)
>
> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> index b35623ae24..113926aff2 100644
> --- a/target/i386/kvm.c
> +++ b/target/i386/kvm.c
> @@ -659,17 +659,41 @@ static int hyperv_handle_properties(CPUState *cs)
> env->features[FEAT_HYPERV_EAX] |= HV_ACCESS_FREQUENCY_MSRS;
> env->features[FEAT_HYPERV_EDX] |= HV_FREQUENCY_MSRS_AVAILABLE;
> }
> - if (cpu->hyperv_crash && has_msr_hv_crash) {
> + if (cpu->hyperv_crash) {
> + if (!has_msr_hv_crash) {
> + fprintf(stderr, "Hyper-V crash MSRs "
> + "(requested by 'hv-crash' cpu flag) "
> + "are not supported by kernel\n");
> + return -ENOSYS;
> + }
> env->features[FEAT_HYPERV_EDX] |= HV_GUEST_CRASH_MSR_AVAILABLE;
> }
> env->features[FEAT_HYPERV_EDX] |= HV_CPU_DYNAMIC_PARTITIONING_AVAILABLE;
> - if (cpu->hyperv_reset && has_msr_hv_reset) {
> + if (cpu->hyperv_reset) {
> + if (!has_msr_hv_reset) {
> + fprintf(stderr, "Hyper-V reset MSR "
> + "(requested by 'hv-reset' cpu flag) "
> + "is not supported by kernel\n");
> + return -ENOSYS;
> + }
> env->features[FEAT_HYPERV_EAX] |= HV_RESET_AVAILABLE;
> }
> - if (cpu->hyperv_vpindex && has_msr_hv_vpindex) {
> + if (cpu->hyperv_vpindex) {
> + if (!has_msr_hv_vpindex) {
> + fprintf(stderr, "Hyper-V VP_INDEX MSR "
> + "(requested by 'hv-vpindex' cpu flag) "
> + "is not supported by kernel\n");
> + return -ENOSYS;
> + }
> env->features[FEAT_HYPERV_EAX] |= HV_VP_INDEX_AVAILABLE;
> }
> - if (cpu->hyperv_runtime && has_msr_hv_runtime) {
> + if (cpu->hyperv_runtime) {
> + if (!has_msr_hv_runtime) {
> + fprintf(stderr, "Hyper-V VP_RUNTIME MSR "
> + "(requested by 'hv-runtime' cpu flag) "
> + "is not supported by kernel\n");
> + return -ENOSYS;
> + }
> env->features[FEAT_HYPERV_EAX] |= HV_VP_RUNTIME_AVAILABLE;
> }
> if (cpu->hyperv_synic) {
> --
> 2.14.3
>
--
Eduardo
