Re: [PATCH v1] s390/kvm: pv: don't present the ecall interrupt twice

[Christian Borntraeger <borntraeger@linux.ibm.com>]

Am 19.07.22 um 10:42 schrieb Janosch Frank:
> On 7/18/22 15:04, Nico Boehr wrote:
>> When the SIGP interpretation facility is present and a VCPU sends an
>> ecall to another VCPU in enabled wait, the sending VCPU receives a 56
>> intercept (partial execution), so KVM can wake up the receiving CPU.
>> Note that the SIGP interpretation facility will take care of the
>> interrupt delivery and KVM's only job is to wake the receiving VCPU.
>>
>> For PV, the sending VCPU will receive a 108 intercept (pv notify) and
>> should continue like in the non-PV case, i.e. wake the receiving VCPU.
>>
>> For PV and non-PV guests the interrupt delivery will occur through the
>> SIGP interpretation facility on SIE entry when SIE finds the X bit in
>> the status field set.
>>
>> However, in handle_pv_notification(), there was no special handling for
>> SIGP, which leads to interrupt injection being requested by KVM for the
>> next SIE entry. This results in the interrupt being delivered twice:
>> once by the SIGP interpretation facility and once by KVM through the
>> IICTL.
>>
>> Add the necessary special handling in handle_pv_notification(), similar
>> to handle_partial_execution(), which simply wakes the receiving VCPU and
>> leave interrupt delivery to the SIGP interpretation facility.
>>
>> In contrast to external calls, emergency calls are not interpreted but
>> also cause a 108 intercept, which is why we still need to call
>> handle_instruction() for SIGP orders other than ecall.
>>
>> Since kvm_s390_handle_sigp_pei() is now called for all SIGP orders which
>> cause a 108 intercept - even if they are actually handled by
>> handle_instruction() - move the tracepoint in kvm_s390_handle_sigp_pei()
>> to avoid possibly confusing trace messages.
> 
> Lengthy but quite informative
> 
>>
>> Signed-off-by: Nico Boehr <nrb@linux.ibm.com>
>> Cc: <stable@vger.kernel.org> # 5.7
>> Fixes: da24a0cc58ed ("KVM: s390: protvirt: Instruction emulation")
> 
> Reviewed-by: Janosch Frank <frankja@linux.ibm.com>

Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>

> 
> Since it already caused confusion:
> I plan on queuing this (via the s390 KVM tree) for 5.20 and not putting it into rc8 since we've been running with this problem for years and I've yet to see a crash because of it.

yes, makes sense.
> 
>> ---
>>   arch/s390/kvm/intercept.c | 15 +++++++++++++++
>>   arch/s390/kvm/sigp.c      |  4 ++--
>>   2 files changed, 17 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c
>> index 8bd42a20d924..88112065d941 100644
>> --- a/arch/s390/kvm/intercept.c
>> +++ b/arch/s390/kvm/intercept.c
>> @@ -528,12 +528,27 @@ static int handle_pv_uvc(struct kvm_vcpu *vcpu)
>>   static int handle_pv_notification(struct kvm_vcpu *vcpu)
>>   {
>> +    int ret;
>> +
>>       if (vcpu->arch.sie_block->ipa == 0xb210)
>>           return handle_pv_spx(vcpu);
>>       if (vcpu->arch.sie_block->ipa == 0xb220)
>>           return handle_pv_sclp(vcpu);
>>       if (vcpu->arch.sie_block->ipa == 0xb9a4)
>>           return handle_pv_uvc(vcpu);
>> +    if (vcpu->arch.sie_block->ipa >> 8 == 0xae) {
>> +        /*
>> +         * Besides external call, other SIGP orders also cause a
>> +         * 108 (pv notify) intercept. In contrast to external call,
>> +         * these orders need to be emulated and hence the appropriate
>> +         * place to handle them is in handle_instruction().
>> +         * So first try kvm_s390_handle_sigp_pei() and if that isn't
>> +         * successful, go on with handle_instruction().
>> +         */
>> +        ret = kvm_s390_handle_sigp_pei(vcpu);
>> +        if (!ret)
>> +            return ret;
>> +    }
>>       return handle_instruction(vcpu);
>>   }
>> diff --git a/arch/s390/kvm/sigp.c b/arch/s390/kvm/sigp.c
>> index 8aaee2892ec3..cb747bf6c798 100644
>> --- a/arch/s390/kvm/sigp.c
>> +++ b/arch/s390/kvm/sigp.c
>> @@ -480,9 +480,9 @@ int kvm_s390_handle_sigp_pei(struct kvm_vcpu *vcpu)
>>       struct kvm_vcpu *dest_vcpu;
>>       u8 order_code = kvm_s390_get_base_disp_rs(vcpu, NULL);
>> -    trace_kvm_s390_handle_sigp_pei(vcpu, order_code, cpu_addr);
>> -
>>       if (order_code == SIGP_EXTERNAL_CALL) {
>> +        trace_kvm_s390_handle_sigp_pei(vcpu, order_code, cpu_addr);
>> +
>>           dest_vcpu = kvm_get_vcpu_by_id(vcpu->kvm, cpu_addr);
>>           BUG_ON(dest_vcpu == NULL);
>