Re: [PATCH v3 07/10] qemu-kvm: Cleanup/fix TSC and PV clock writeback

Marcelo Tosatti
2010-02-24T23:28:22Z

On Wed, Feb 24, 2010 at 03:17:55PM +0100, Jan Kiszka wrote:
> Drop kvm_load_tsc in favor of level-dependent writeback in
> kvm_arch_load_regs. KVM's PV clock MSRs fall in the same category and
> should therefore only be written back on full sync.
>
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
> qemu-kvm-x86.c | 19 +++++--------------
> qemu-kvm.h | 4 ----
> target-i386/machine.c | 5 -----
> 3 files changed, 5 insertions(+), 23 deletions(-)
>
> diff --git a/qemu-kvm-x86.c b/qemu-kvm-x86.c
> index 840c1c9..84fd7fa 100644
> --- a/qemu-kvm-x86.c
> +++ b/qemu-kvm-x86.c
> @@ -965,8 +965,11 @@ void kvm_arch_load_regs(CPUState *env, int level)
> set_msr_entry(&msrs[n++], MSR_LSTAR , env->lstar);
> }
> #endif
> - set_msr_entry(&msrs[n++], MSR_KVM_SYSTEM_TIME, env->system_time_msr);
> - set_msr_entry(&msrs[n++], MSR_KVM_WALL_CLOCK, env->wall_clock_msr);
> + if (level == KVM_PUT_FULL_STATE) {
> + set_msr_entry(&msrs[n++], MSR_IA32_TSC, env->tsc);
> + set_msr_entry(&msrs[n++], MSR_KVM_SYSTEM_TIME, env->system_time_msr);
> + set_msr_entry(&msrs[n++], MSR_KVM_WALL_CLOCK, env->wall_clock_msr);
> + }

As things stand today, the TSC should only be written on migration. See
53f658b3c33616a4997ee254311b335e59063289 in the kernel.