linux-kernel - Re: [PATCH 19/32] KVM: s390: mechanism to enable guest zPCI Interpretation

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Message-ID: <6127b774-1042-0057-6b5b-29471554149b@linux.ibm.com>
Date:   Fri, 10 Dec 2021 09:21:47 -0500
From:   Matthew Rosato <mjrosato@...ux.ibm.com>
To:     Christian Borntraeger <borntraeger@...ux.ibm.com>,
        linux-s390@...r.kernel.org
Cc:     alex.williamson@...hat.com, cohuck@...hat.com,
        schnelle@...ux.ibm.com, farman@...ux.ibm.com, pmorel@...ux.ibm.com,
        hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, agordeev@...ux.ibm.com,
        frankja@...ux.ibm.com, david@...hat.com, imbrenda@...ux.ibm.com,
        vneethv@...ux.ibm.com, oberpar@...ux.ibm.com, freude@...ux.ibm.com,
        thuth@...hat.com, pasic@...ux.ibm.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 19/32] KVM: s390: mechanism to enable guest zPCI
 Interpretation

On 12/10/21 8:27 AM, Christian Borntraeger wrote:
> 
> 
> Am 07.12.21 um 21:57 schrieb Matthew Rosato:
>> The guest must have access to certain facilities in order to allow
>> interpretive execution of zPCI instructions and adapter event
>> notifications.  However, there are some cases where a guest might
>> disable interpretation -- provide a mechanism via which we can defer
>> enabling the associated zPCI interpretation facilities until the guest
>> indicates it wishes to use them.
>>
>> Signed-off-by: Matthew Rosato <mjrosato@...ux.ibm.com>
>> ---
>>   arch/s390/include/asm/kvm_host.h |  4 +++
>>   arch/s390/kvm/kvm-s390.c         | 43 ++++++++++++++++++++++++++++++++
>>   arch/s390/kvm/kvm-s390.h         | 10 ++++++++
>>   3 files changed, 57 insertions(+)
>>
>> diff --git a/arch/s390/include/asm/kvm_host.h 
>> b/arch/s390/include/asm/kvm_host.h
>> index 3f147b8d050b..38982c1de413 100644
>> --- a/arch/s390/include/asm/kvm_host.h
>> +++ b/arch/s390/include/asm/kvm_host.h
>> @@ -252,7 +252,10 @@ struct kvm_s390_sie_block {
>>   #define ECB2_IEP    0x20
>>   #define ECB2_PFMFI    0x08
>>   #define ECB2_ESCA    0x04
>> +#define ECB2_ZPCI_LSI    0x02
>>       __u8    ecb2;                   /* 0x0062 */
>> +#define ECB3_AISI    0x20
>> +#define ECB3_AISII    0x10
>>   #define ECB3_DEA 0x08
>>   #define ECB3_AES 0x04
>>   #define ECB3_RI  0x01
>> @@ -938,6 +941,7 @@ struct kvm_arch{
>>       int use_cmma;
>>       int use_pfmfi;
>>       int use_skf;
>> +    int use_zpci_interp;
>>       int user_cpu_state_ctrl;
>>       int user_sigp;
>>       int user_stsi;
>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
>> index a680f2a02b67..361d742cdf0d 100644
>> --- a/arch/s390/kvm/kvm-s390.c
>> +++ b/arch/s390/kvm/kvm-s390.c
>> @@ -1023,6 +1023,47 @@ static int kvm_s390_vm_set_crypto(struct kvm 
>> *kvm, struct kvm_device_attr *attr)
>>       return 0;
>>   }
>> +static void kvm_s390_vcpu_pci_setup(struct kvm_vcpu *vcpu)
>> +{
>> +    /*
>> +     * If the facilities aren't available for PCI interpretation and
>> +     * interrupt forwarding, we shouldn't be here.
>> +     */
> 
> This reads like we want a WARN_ON or BUG_ON, but as we call this 
> uncoditionally this is
> actually a valid check. So instead of "shouldn't be here" say something 
> like "bail out
> if interpretion is not active".  ?

Right, this comment block is plain wrong.  We expect to get here under 
multiple circumstances and its OK for this bit to be off:
- initial vcpu setup (use_zpci_interp is off)
- Right after we set use_zpci_interp=1 (turn on ECB for all vcpu)
- hotplug vcpu setup (use_zpci_interp might be on or off)

Will re-word.

> 
>> +    if (!vcpu->kvm->arch.use_zpci_interp)
>> +        return;
>> +
>> +    vcpu->arch.sie_block->ecb2 |= ECB2_ZPCI_LSI;
>> +    vcpu->arch.sie_block->ecb3 |= ECB3_AISII + ECB3_AISI;
>> +}
>> +
>> +void kvm_s390_vcpu_pci_enable_interp(struct kvm *kvm)
>> +{
>> +    struct kvm_vcpu *vcpu;
>> +    int i;
>> +
>> +    /*
>> +     * If host facilities are available, turn on interpretation for the
>> +     * life of this guest
>> +     */
>> +    if (!test_facility(69) || !test_facility(70) || 
>> !test_facility(71) ||
>> +        !test_facility(72))
>> +        return;
> 
> Wouldnt that also enable interpretion for VSIE? I guess we should check 
> for the
> sclp facilities from patches 1,2,3, and 4 instead.
> 

Good point -- will change.