On 18.01.21 14:45, Janosch Frank wrote:
> On 1/18/21 2:17 PM, Christian Borntraeger 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.
>
> Before Conny starts yelling I'll do it myself:
> Documentation
>
>>
>> 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(-)
>>
>> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
>> index 74f9a036bab2..98ae55f79620 100644
>> --- a/arch/s390/include/asm/kvm_host.h
>> +++ b/arch/s390/include/asm/kvm_host.h
>> @@ -455,6 +455,7 @@ struct kvm_vcpu_stat {
>> u64 diagnose_44;
>> u64 diagnose_9c;
>> u64 diagnose_9c_ignored;
>> + u64 diagnose_9c_forward;
>> u64 diagnose_258;
>> u64 diagnose_308;
>> u64 diagnose_500;
>> diff --git a/arch/s390/include/asm/smp.h b/arch/s390/include/asm/smp.h
>> index 01e360004481..e317fd4866c1 100644
>> --- a/arch/s390/include/asm/smp.h
>> +++ b/arch/s390/include/asm/smp.h
>> @@ -63,5 +63,6 @@ extern void __noreturn cpu_die(void);
>> extern void __cpu_die(unsigned int cpu);
>> extern int __cpu_disable(void);
>> extern void schedule_mcck_handler(void);
>> +void notrace smp_yield_cpu(int cpu);
>>
>> #endif /* __ASM_SMP_H */
>> diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
>> index c5abbb94ac6e..32622e9c15f0 100644
>> --- a/arch/s390/kernel/smp.c
>> +++ b/arch/s390/kernel/smp.c
>> @@ -422,6 +422,7 @@ void notrace smp_yield_cpu(int cpu)
>> asm volatile("diag %0,0,0x9c"
>> : : "d" (pcpu_devices[cpu].address));
>> }
>> +EXPORT_SYMBOL(smp_yield_cpu);
>>
>> /*
>> * Send cpus emergency shutdown signal. This gives the cpus the
>> diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c
>> index 5b8ec1c447e1..fc1ec4aa81ed 100644
>> --- a/arch/s390/kvm/diag.c
>> +++ b/arch/s390/kvm/diag.c
>> @@ -150,6 +150,19 @@ static int __diag_time_slice_end(struct kvm_vcpu *vcpu)
>> return 0;
>> }
>>
>> +static unsigned int forward_cnt;
>
> This is not per CPU, so we could have one CPU making forwards impossible
> for all others, right? Would this be a possible improvement or doesn't
> that happen in real world workloads?
this is mostly a system limit to avoid non-root users being able to trigger
gazillions of diag9c hypercalls.
