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

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Message-ID: <cd5ac83e-76b5-178b-fd9a-b651ae9dbcca@linux.ibm.com>
Date:   Tue, 14 Dec 2021 18:04:01 +0100
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Matthew Rosato <mjrosato@...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 12/7/21 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.

> +	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.

> +		kvm_s390_set_psw_cc(vcpu, 1);
> +		break;
> +	}

NIT: This switch above could be much more simple if you set CC after the 
switch.

> +
> +	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;
>   	}
> 





-- 
Pierre Morel
IBM Lab Boeblingen