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:
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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