linux-kernel - Re: [PATCH 24/32] KVM: s390: intercept the rpcit instruction

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Date:   Tue, 14 Dec 2021 13:00:00 -0500
From:   Matthew Rosato <mjrosato@...ux.ibm.com>
To:     Pierre Morel <pmorel@...ux.ibm.com>, linux-s390@...r.kernel.org
Cc:     alex.williamson@...hat.com, cohuck@...hat.com,
        schnelle@...ux.ibm.com, farman@...ux.ibm.com,
        borntraeger@...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 24/32] KVM: s390: intercept the rpcit instruction

On 12/14/21 12:04 PM, Pierre Morel wrote:
> 
> 
> On 12/7/21 21:57, Matthew Rosato wrote:
>> For faster handling of PCI translation refreshes, intercept in KVM
>> and call the associated handler.
>>
>> Signed-off-by: Matthew Rosato <mjrosato@...ux.ibm.com>
>> ---
>>   arch/s390/kvm/pci.h  |  4 ++++
>>   arch/s390/kvm/priv.c | 41 +++++++++++++++++++++++++++++++++++++++++
>>   2 files changed, 45 insertions(+)
>>
>> diff --git a/arch/s390/kvm/pci.h b/arch/s390/kvm/pci.h
>> index d252a631b693..3f96eff432aa 100644
>> --- a/arch/s390/kvm/pci.h
>> +++ b/arch/s390/kvm/pci.h
>> @@ -18,6 +18,10 @@
>>   #define KVM_S390_PCI_DTSM_MASK 0x40
>> +#define KVM_S390_RPCIT_STAT_MASK 0xffffffff00ffffffUL
>> +#define KVM_S390_RPCIT_INS_RES (0x10 << 24)
>> +#define KVM_S390_RPCIT_ERR (0x28 << 24)
> 
> I
> 
>> +
>>   struct zpci_gaite {
>>       unsigned int gisa;
>>       u8 gisc;
>> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
>> index 417154b314a6..768ae92ecc59 100644
>> --- a/arch/s390/kvm/priv.c
>> +++ b/arch/s390/kvm/priv.c
>> @@ -29,6 +29,7 @@
>>   #include <asm/ap.h>
>>   #include "gaccess.h"
>>   #include "kvm-s390.h"
>> +#include "pci.h"
>>   #include "trace.h"
>>   static int handle_ri(struct kvm_vcpu *vcpu)
>> @@ -335,6 +336,44 @@ static int handle_rrbe(struct kvm_vcpu *vcpu)
>>       return 0;
>>   }
>> +static int handle_rpcit(struct kvm_vcpu *vcpu)
>> +{
>> +    int reg1, reg2;
>> +    int rc;
>> +
>> +    if (vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE)
>> +        return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP);
>> +
>> +    kvm_s390_get_regs_rre(vcpu, &reg1, &reg2);
>> +
> 
> I would prefer to take care of the interception immediately here
> 
>          fh = vcpu->run->s.regs.gprs[reg1] >> 32;
>          if ((fh & aift.mdd) != 0)
>                  return -EOPNOTSUP
> 
> instead of doing it inside kvm_s390_pci_refresh_trans.
> It would simplify in my opinion.

OK

> 
>> +    rc = kvm_s390_pci_refresh_trans(vcpu, vcpu->run->s.regs.gprs[reg1],
>> +                    vcpu->run->s.regs.gprs[reg2],
>> +                    vcpu->run->s.regs.gprs[reg2+1]);
>> +
> 
> 
>> +    switch (rc) {
>> +    case 0:
>> +        kvm_s390_set_psw_cc(vcpu, 0);
>> +        break;
>> +    case -EOPNOTSUPP:
>> +        return -EOPNOTSUPP;
>> +    case -EINVAL:
>> +        kvm_s390_set_psw_cc(vcpu, 3);
>> +        break;
>> +    case -ENOMEM:
>> +        vcpu->run->s.regs.gprs[reg1] &= KVM_S390_RPCIT_STAT_MASK;
>> +        vcpu->run->s.regs.gprs[reg1] |= KVM_S390_RPCIT_INS_RES;
>> +        kvm_s390_set_psw_cc(vcpu, 1);
>> +        break;
>> +    default:
>> +        vcpu->run->s.regs.gprs[reg1] &= KVM_S390_RPCIT_STAT_MASK;
>> +        vcpu->run->s.regs.gprs[reg1] |= KVM_S390_RPCIT_ERR;
> 
> I think you should use the status reported by the hardware, reporting 
> "Error recovery in progress" what ever the hardware error was does not 
> seem right.
> 

OK, this ties into your other comment about calling __rpcit() directly 
so we have a status to look at -- will look into it

>> +        kvm_s390_set_psw_cc(vcpu, 1);
>> +        break;
>> +    }
> 
> NIT: This switch above could be much more simple if you set CC after the 
> switch.

We are setting 3 different CCs over 4 cases, so there's only 1 
duplication in the switch, so I'm not sure how much simpler?

But anyway this might not be relevant if I change to call __rpcit() 
directly.

> 
>> +
>> +    return 0;
>> +}
>> +
>>   #define SSKE_NQ 0x8
>>   #define SSKE_MR 0x4
>>   #define SSKE_MC 0x2
>> @@ -1275,6 +1314,8 @@ int kvm_s390_handle_b9(struct kvm_vcpu *vcpu)
>>           return handle_essa(vcpu);
>>       case 0xaf:
>>           return handle_pfmf(vcpu);
>> +    case 0xd3:
>> +        return handle_rpcit(vcpu);
>>       default:
>>           return -EOPNOTSUPP;
>>       }
>>
> 
> 
> 
> 
>