On Mon, 18 Jan 2021 14:17:39 +0100
Christian Borntraeger <borntraeger@xxxxxxxxxx> wrote:
> From: Pierre Morel <pmorel@xxxxxxxxxxxxx>
>
> When we receive intercept a DIAG_9C from the guest we verify
> that the target real CPU associated with the virtual CPU
> designated by the guest is running and if not we forward the
> DIAG_9C to the target real CPU.
>
> To avoid a diag9c storm we allow a maximal rate of diag9c forwarding.
>
> The rate is calculated as a count per second defined as a
> new parameter of the s390 kvm module: diag9c_forwarding_hz .
>
> The default value is to not forward diag9c.
>
> Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
> Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> ---
> arch/s390/include/asm/kvm_host.h | 1 +
> arch/s390/include/asm/smp.h | 1 +
> arch/s390/kernel/smp.c | 1 +
> arch/s390/kvm/diag.c | 31 ++++++++++++++++++++++++++++---
> arch/s390/kvm/kvm-s390.c | 6 ++++++
> arch/s390/kvm/kvm-s390.h | 8 ++++++++
> 6 files changed, 45 insertions(+), 3 deletions(-)
>
(...)
> @@ -167,9 +180,21 @@ static int __diag_time_slice_end_directed(struct kvm_vcpu *vcpu)
> if (!tcpu)
> goto no_yield;
>
> - /* target already running */
> - if (READ_ONCE(tcpu->cpu) >= 0)
> - goto no_yield;
> + /* target VCPU already running */
Maybe make this /* target guest VPCU already running */...
> + if (READ_ONCE(tcpu->cpu) >= 0) {
> + if (!diag9c_forwarding_hz || diag9c_forwarding_overrun())
> + goto no_yield;
> +
> + /* target CPU already running */
...and this /* target host CPU already running */? I just read this
several times and was confused before I spotted the difference :)
> + if (!vcpu_is_preempted(tcpu->cpu))
> + goto no_yield;
> + smp_yield_cpu(tcpu->cpu);
> + VCPU_EVENT(vcpu, 5,
> + "diag time slice end directed to %d: yield forwarded",
> + tid);
> + vcpu->stat.diagnose_9c_forward++;
> + return 0;
> + }
>
> if (kvm_vcpu_yield_to(tcpu) <= 0)
> goto no_yield;
(...)
