On Tue, Feb 10, 2015 at 01:46:15PM +0100, Paolo Bonzini wrote:
> From: Marcelo Tosatti <[email protected]>
>
> [ Upstream commit 7f187922ddf6b67f2999a76dcb71663097b75497 ]
>
> When the guest writes to the TSC, the masterclock TSC copy must be
> updated as well along with the TSC_OFFSET update, otherwise a negative
> tsc_timestamp is calculated at kvm_guest_time_update.
>
> Once "if (!vcpus_matched && ka->use_master_clock)" is simplified to
> "if (ka->use_master_clock)", the corresponding "if (!ka->use_master_clock)"
> becomes redundant, so remove the do_request boolean and collapse
> everything into a single condition.
>
> Signed-off-by: Marcelo Tosatti <[email protected]>
> Signed-off-by: Paolo Bonzini <[email protected]>
> ---
> Without this patch, latest userspace triggers an assertion.
Thanks, it seems to be applicable to the 3.16 so I'm queuing it for
this kernel.
Cheers,
--
Luís
>
> arch/x86/kvm/x86.c | 19 ++++++++++---------
> 1 file changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index da1591eeb477..e0260ccd78a4 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1235,21 +1235,22 @@ void kvm_track_tsc_matching(struct kvm_vcpu *vcpu)
> {
> #ifdef CONFIG_X86_64
> bool vcpus_matched;
> - bool do_request = false;
> struct kvm_arch *ka = &vcpu->kvm->arch;
> struct pvclock_gtod_data *gtod = &pvclock_gtod_data;
>
> vcpus_matched = (ka->nr_vcpus_matched_tsc + 1 ==
> atomic_read(&vcpu->kvm->online_vcpus));
>
> - if (vcpus_matched && gtod->clock.vclock_mode == VCLOCK_TSC)
> - if (!ka->use_master_clock)
> - do_request = 1;
> -
> - if (!vcpus_matched && ka->use_master_clock)
> - do_request = 1;
> -
> - if (do_request)
> + /*
> + * Once the masterclock is enabled, always perform request in
> + * order to update it.
> + *
> + * In order to enable masterclock, the host clocksource must be TSC
> + * and the vcpus need to have matched TSCs. When that happens,
> + * perform request to enable masterclock.
> + */
> + if (ka->use_master_clock ||
> + (gtod->clock.vclock_mode == VCLOCK_TSC && vcpus_matched))
> kvm_make_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu);
>
> trace_kvm_track_tsc(vcpu->vcpu_id, ka->nr_vcpus_matched_tsc,
> --
> 2.1.0
>
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