On Tue, 2011-02-01 at 21:26 +0100, Jan Kiszka wrote:
> On 2011-02-01 20:17, Glauber Costa wrote:
> > If the machine is stopped, we should not record two different tsc values
> > upon a save operation. The same problem happens with kvmclock.
> >
> > But kvmclock is taking a different diretion, being now seen as a separate
> > device. Since this is unlikely to happen with the tsc, I am taking the
> > approach here of simply registering a handler for state change, and
> > using a per-CPUState variable that prevents double updates for the TSC.
> >
> > Signed-off-by: Glauber Costa <glommer@xxxxxxxxxx>
> > ---
> > target-i386/cpu.h | 1 +
> > target-i386/kvm.c | 19 ++++++++++++++++++-
> > 2 files changed, 19 insertions(+), 1 deletions(-)
> >
> > diff --git a/target-i386/cpu.h b/target-i386/cpu.h
> > index 6d619e8..7f1c4f8 100644
> > --- a/target-i386/cpu.h
> > +++ b/target-i386/cpu.h
> > @@ -732,6 +732,7 @@ typedef struct CPUX86State {
> > uint32_t sipi_vector;
> > uint32_t cpuid_kvm_features;
> > uint32_t cpuid_svm_features;
> > + uint8_t update_tsc;
>
> bool please.
>
> >
> > /* in order to simplify APIC support, we leave this pointer to the
> > user */
> > diff --git a/target-i386/kvm.c b/target-i386/kvm.c
> > index ecb8405..c3925be 100644
> > --- a/target-i386/kvm.c
> > +++ b/target-i386/kvm.c
> > @@ -302,6 +302,16 @@ void kvm_inject_x86_mce(CPUState *cenv, int bank, uint64_t status,
> >
> > static int _kvm_arch_init_vcpu(CPUState *env);
> >
> > +static void cpu_update_state(void *opaque, int running, int reason)
> > +{
> > + CPUState *env = opaque;
> > +
> > + if (!running) {
> > + env->update_tsc = 1;
> > + }
> > +}
> > +
> > +
>
> Additional blank line.
>
> > int kvm_arch_init_vcpu(CPUState *env)
> > {
> > int r;
> > @@ -444,6 +454,8 @@ int kvm_arch_init_vcpu(CPUState *env)
> > }
> > #endif
> >
> > + qemu_add_vm_change_state_handler(cpu_update_state, env);
> > +
> > return kvm_vcpu_ioctl(env, KVM_SET_CPUID2, &cpuid_data);
> > }
> >
> > @@ -1093,7 +1105,12 @@ static int kvm_get_msrs(CPUState *env)
> > msrs[n++].index = MSR_STAR;
> > if (kvm_has_msr_hsave_pa(env))
> > msrs[n++].index = MSR_VM_HSAVE_PA;
> > - msrs[n++].index = MSR_IA32_TSC;
> > +
> > + if (env->update_tsc) {
> > + msrs[n++].index = MSR_IA32_TSC;
> > + env->update_tsc = 0;
> > + }
> > +
> > #ifdef TARGET_X86_64
> > if (lm_capable_kernel) {
> > msrs[n++].index = MSR_CSTAR;
>
> Not quite the logic I'm using for kvmclock:
Ok. I have all the interest in keeping the same logic.
I will respin.
> cpu_update_state()
> if running
> tsc_valid = false;
>
> kvm_get_msrs()
> ...
> if (!tsc_valid)
> read_tsc
> tsc_valid = !vm_running;
>
> That ensure we always read the tsc while the VM is running, and not only
> after it was stopped (might otherwise be "surprising" when once
> visualizing the MSRs).
>
> Jan
>
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