Re: [Qemu-devel] target-i386: block migration and savevm if invariant tsc is exposed (v3)

[Eduardo Habkost]

On Wed, Apr 23, 2014 at 06:04:45PM -0300, Marcelo Tosatti wrote:
> 
> Invariant TSC documentation mentions that "invariant TSC will run at a
> constant rate in all ACPI P-, C-. and T-states".
> 
> This is not the case if migration to a host with different TSC frequency 
> is allowed, or if savevm is performed. So block migration/savevm.
> 
> Signed-off-by: Marcelo Tosatti <address@hidden>
> 
[...]
> @@ -702,6 +706,16 @@ int kvm_arch_init_vcpu(CPUState *cs)
>                                    !!(c->ecx & CPUID_EXT_SMX);
>      }
>  
> +    c = cpuid_find_entry(&cpuid_data.cpuid, 0x80000007, 0);
> +    if (c && (c->edx & 1<<8) && invtsc_mig_blocker == NULL) {
> +        /* for migration */
> +        error_set(&invtsc_mig_blocker,
> +                  QERR_DEVICE_FEATURE_BLOCKS_MIGRATION, "invtsc", "cpu");
> +        migrate_add_blocker(invtsc_mig_blocker);
> +        /* for savevm */
> +        vmstate_x86_cpu.unmigratable = 1;

Did you ensure this will always happen before vmstate_register() is
called for vmstate_x86_cpu? I believe kvm_arch_init_vcpu() is called a
long long time after device_set_realized() (which is where
vmstate_register() is called for DeviceState objects).

-- 
Eduardo